1
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Kranabetter L, Kristensen HH, Schouder CA, Stapelfeldt H. Structure determination of alkali trimers on helium nanodroplets through laser-induced Coulomb explosion. J Chem Phys 2024; 160:131101. [PMID: 38557840 DOI: 10.1063/5.0200389] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2024] [Accepted: 03/15/2024] [Indexed: 04/04/2024] Open
Abstract
Alkali trimers, Ak3, located on the surface of He nanodroplets are triply ionized following multiphoton absorption from an intense femtosecond laser pulse, leading to fragmentation into three correlated Ak+ ions. Combining the information from threefold covariance analysis of the emission direction of the fragment ions and their kinetic energy distributions P(Ekin), we find that Na3, K3, and Rb3 have an equilateral triangular structure, corresponding to that of the lowest lying quartet state A2'4, and determine the equilibrium bond distance Req(Na3) = 4.65 ± 0.15 Å, Req(K3) = 5.03 ± 0.18 Å, and Req(Rb3) = 5.45 ± 0.22 Å. For K3 and Rb3, these values agree well with existing theoretical calculations, while for Na3, the value is 0.2-0.3 Å larger than the existing theoretical results. The discrepancy is ascribed to a minor internuclear motion of Na3 during the ionization process. In addition, we determine the distribution of internuclear distances P(R) under the assumption of fixed bond angles. The results are compared to the square of the internuclear wave function |Ψ(R)|2.
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Affiliation(s)
- Lorenz Kranabetter
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
| | - Henrik H Kristensen
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
| | - Constant A Schouder
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
- LIDYL, CNRS, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
| | - Henrik Stapelfeldt
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
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2
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Shaik S, Danovich D, Hiberty PC. On The Nature of the Chemical Bond in Valence Bond Theory. J Chem Phys 2022; 157:090901. [DOI: 10.1063/5.0095953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
This perspective outlines a panoramic description of the nature of the chemical bond according to valence bond theory. It describes single bonds, and charge-shift bonds (CSBs) in which the entire/most of the bond energy arises from the resonance between the covalent and ionic structures of the bond. Many CSBs are homonuclear bonds. Hypervalent molecules are CSBs. Then we describe multiply bonded molecules with emphasis on C2 and 3O2. The perspective outlines an effective methodology of peeling the electronic structure to the necessary minimum: a structure with a quadruple bond, and two minor structures with double bonds, which stabilize the quadruple bond by resonance. 3O2 is chosen because it is a persistent diradical. The persistence of 3O2 is due to the large CSB resonance interaction of the π-3-electron bonds. Subsequently, we describe the roles of π vs. σ in the geometric preferences in unsaturated molecules, and their Si-based analogs. Then, the perspective discusses bonding in clusters of univalent metal-atoms, which possess only parallel spins, and are nevertheless bonded due to multiple resonance interactions. The bond energy reaches ~40 kcal/mol for a pair of atoms (in n+1Cun; n~10-12). The final subsection discusses singlet excited states in ethene, ozone and SO2. It demonstrates the capability of the breathing-orbital VB method to yield an accurate description of a variety of excited states using 10 or less VB structures. Furthermore, the method underscores covalent structures which play a key role in the correct description and bonding of these excited states.
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Affiliation(s)
- Sason Shaik
- Hebrew University of Jerusalem Institute of Chemistry, Israel
| | - David Danovich
- Hebrew University of Jerusalem Institute of Chemistry, Israel
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3
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Kristensen HH, Kranabetter L, Schouder CA, Stapper C, Arlt J, Mudrich M, Stapelfeldt H. Quantum-State-Sensitive Detection of Alkali Dimers on Helium Nanodroplets by Laser-Induced Coulomb Explosion. PHYSICAL REVIEW LETTERS 2022; 128:093201. [PMID: 35302820 DOI: 10.1103/physrevlett.128.093201] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Revised: 01/21/2022] [Accepted: 02/10/2022] [Indexed: 06/14/2023]
Abstract
Rubidium dimers residing on the surface of He nanodroplets are doubly ionized by an intense femtosecond laser pulse leading to fragmentation into a pair of Rb^{+} ions. We show that the kinetic energy of the Rb^{+} fragment ions can be used to identify dimers formed in either the X ^{1}Σ_{g}^{+} ground state or in the lowest-lying triplet state, a ^{3}Σ_{u}^{+}. From the experiment, we estimate the abundance ratio of dimers in the a and X states as a function of the mean droplet size and find values between 4∶1 and 5∶1. Our technique applies generally to dimers and trimers of alkali atoms, here also demonstrated for Li_{2}, Na_{2}, and K_{2}, and will enable femtosecond time-resolved measurements of their rotational and vibrational dynamics, possibly with atomic structural resolution.
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Affiliation(s)
- Henrik H Kristensen
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
| | - Lorenz Kranabetter
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
| | - Constant A Schouder
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
| | - Christoph Stapper
- Faculty of Chemistry and Pharmacy, University of Würzburg, Am Hubland, Campus Süd, D-97074 Würzburg, Germany
| | - Jacqueline Arlt
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
| | - Marcel Mudrich
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
| | - Henrik Stapelfeldt
- Department of Chemistry, Aarhus University, Langelandsgade 140, DK-8000 Aarhus C, Denmark
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4
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Zhao W, Li Q, Huang XH, Bie LH, Gao J. Toward the Prediction of Multi-Spin State Charges of a Heme Model by Random Forest Regression. Front Chem 2020; 8:162. [PMID: 32296675 PMCID: PMC7136535 DOI: 10.3389/fchem.2020.00162] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 02/24/2020] [Indexed: 11/13/2022] Open
Abstract
The random forest regression (RFR) model was introduced to predict the multiple spin state charges of a heme model, which is important for the molecular dynamic simulation of the spin crossover phenomenon. In this work, a multiple spin state structure data set with 39,368 structures of the simplified heme-oxygen binding model was built from the non-adiabatic dynamic simulation trajectories. The ESP charges of each atom were calculated and used as the real-valued response. The conformational adapted charge model (CAC) of three spin states was constructed by an RFR model using symmetry functions. The results show that our RFR model can effectively predict the on the fly atomic charges with the varying conformations as well as the atomic charge of different spin states in the same conformation, thus achieving the balance of accuracy and efficiency. The average mean absolute error of the predicted charges of each spin state is <0.02 e. The comparison studies on descriptors showed a maximum 0.06 e improvement in prediction of the charge of Fe 2+ by using 11 manually selected structural parameters. We hope that this model can not only provide variable parameters for developing the force field of the multi-spin state but also facilitate automation, thus enabling large-scale simulations of atomistic systems.
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Affiliation(s)
| | | | | | - Li-Hua Bie
- Hubei Key Laboratory of Agricultural Bioinformatics, College of Informatics, Huazhong Agricultural University, Wuhan, China
| | - Jun Gao
- Hubei Key Laboratory of Agricultural Bioinformatics, College of Informatics, Huazhong Agricultural University, Wuhan, China
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5
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Lackner F, Ernst WE. Photoinduced Molecule Formation of Spatially Separated Atoms on Helium Nanodroplets. J Phys Chem Lett 2018; 9:3561-3566. [PMID: 29893573 DOI: 10.1021/acs.jpclett.8b01530] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Besides the use as cold matrix for spectroscopic studies, superfluid helium droplets have served as a cold environment for the synthesis of molecules and clusters. Since vibrational frequencies of molecules in helium droplets exhibit almost no shift compared to the free molecule values, one could assume the solvated particles move frictionless and undergo a reaction as soon as their paths cross. There have been a few unexplained observations that seemed to indicate cases of two species on one droplet not forming bonds but remaining isolated. In this work, we performed a systematic study of helium droplets doped with one rubidium and one strontium atom showing that besides a reaction to RbSr, there is a probability of finding separated Rb and Sr atoms on one droplet that only react after electronic excitation. Our results further indicate that ground-state Sr atoms can reside at the surface as well as inside the droplet.
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Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics , Graz University of Technology , Petersgasse 16 , A-8010 Graz , Austria, European Union
| | - Wolfgang E Ernst
- Institute of Experimental Physics , Graz University of Technology , Petersgasse 16 , A-8010 Graz , Austria, European Union
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6
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Lackner F, Krois G, Ernst WE. Lithium atoms on helium nanodroplets: Rydberg series and ionization dynamics. J Chem Phys 2018; 147:184302. [PMID: 29141430 DOI: 10.1063/1.5004543] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The electronic excitation spectrum of lithium atoms residing on the surface of helium nanodroplets is presented and analyzed employing a Rydberg-Ritz approach. Utilizing resonant two-photon ionization spectroscopy, two different Rydberg series have been identified: one assigned to the nS(Σ) series and the other with predominantly nP(Π) character. For high Rydberg states, which have been resolved up to n = 13, the surrounding helium effectively screens the valence electron from the Li ion core, as indicated by the apparent red-shift of Li transitions and lowered quantum defects on the droplet with respect to their free atom counterparts. For low n states, the screening effect is weakened and the prevailing repulsive interaction gives rise to strongly broadened and blue-shifted transitions. The red-shifts originate from the polarization of nearby He atoms by the positive Li ion core. As a consequence of this effect, the ionization threshold is lowered by 116 ± 10 cm-1 for Li on helium droplets with a radius of about 40 Å. Upon single-photon ionization, heavy complexes corresponding to Li ions attached to intact helium droplets are detected. We conclude that ionization close to the on-droplet ionization threshold triggers a dynamic process in which the Li ion core undergoes a transition from a surface site into the droplet.
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Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Günter Krois
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Wolfgang E Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
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7
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Jasik P, Kilich T, Kozicki J, Sienkiewicz J. Potential energy surfaces of the low-lying electronic states of the Li + LiCs system. Chem Phys Lett 2018. [DOI: 10.1016/j.cplett.2018.02.005] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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8
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Hauser AW, de Lara-Castells MP. Spatial quenching of a molecular charge-transfer process in a quantum fluid: the Cs x-C 60 reaction in superfluid helium nanodroplets. Phys Chem Chem Phys 2017; 19:1342-1351. [PMID: 27975088 DOI: 10.1039/c6cp06858h] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A recent experimental study [Renzler et al., J. Chem. Phys., 2016, 145, 181101] on superfluid helium nanodroplets reported different reactivities for Cs atoms and Cs2 dimers with C60 fullerenes inside helium droplets. Alkali metal atoms and clusters are heliophobic, therefore typically residing on the droplet surface, while fullerenes are fully immersed into the droplet. In this theoretical study, which combines standard methods of computational chemistry with orbital-free helium density functional theory, we show that the experimental findings can be interpreted in the light of a quenched electron-transfer reaction between the fullerene and the alkali dopant, which is additionally hindered by a reaction barrier stemming from the necessary extrusion of helium upon approach of the two reactants.
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Affiliation(s)
- Andreas W Hauser
- Graz University of Technology, Institute of Experimental Physics, Petersgasse 16, 8010 Graz, Austria.
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9
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Sieg A, von Vangerow J, Stienkemeier F, Dulieu O, Mudrich M. Desorption Dynamics of Rb 2 Molecules Off the Surface of Helium Nanodroplets. J Phys Chem A 2016; 120:7641-7649. [PMID: 27606714 DOI: 10.1021/acs.jpca.6b05732] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The desorption dynamics of rubidium dimers (Rb2) off the surface of helium nanodroplets induced by laser excitation is studied by employing both nanosecond and femtosecond ion imaging spectroscopy. Similarly to alkali metal atoms, we find that the Rb2 desorption process resembles the dissociation of a diatomic molecule. However, both angular and energy distributions of detected Rb2+ ions appear to be most crucially determined by the Rb2 intramolecular degrees of freedom rather than by those of the Rb2HeN complex. The pump-probe dynamics of Rb2+ is found to be slower than that of Rb+, pointing at a weaker effective guest-host repulsion for excited molecules than for single atoms.
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Affiliation(s)
- A Sieg
- Physikalisches Institut, Universität Freiburg , 79104 Freiburg, Germany
| | - J von Vangerow
- Physikalisches Institut, Universität Freiburg , 79104 Freiburg, Germany
| | - F Stienkemeier
- Physikalisches Institut, Universität Freiburg , 79104 Freiburg, Germany
| | - O Dulieu
- Laboratoire Aimé Cotton, CNRS, Université Paris-Sud, ENS Cachan, Université Paris-Saclay , 91405 Orsay Cedex, France
| | - M Mudrich
- Physikalisches Institut, Universität Freiburg , 79104 Freiburg, Germany
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10
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Pototschnig JV, Krois G, Lackner F, Ernst WE. Investigation of the RbCa molecule: Experiment and theory. JOURNAL OF MOLECULAR SPECTROSCOPY 2015; 310:126-134. [PMID: 25922550 PMCID: PMC4407902 DOI: 10.1016/j.jms.2015.01.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 01/12/2015] [Indexed: 06/04/2023]
Abstract
We present a thorough theoretical and experimental study of the electronic structure of RbCa. The mixed alkali-alkaline earth molecule RbCa was formed on superfluid helium nanodroplets. Excited states of the molecule in the range of 13 000-23 000 cm-1 were recorded by resonance enhanced multi-photon ionization time-of-flight spectroscopy. The experiment is accompanied by high level ab initio calculations of ground and excited state properties, utilizing a multireference configuration interaction method based on multiconfigurational self consistent field calculations. With this approach the potential energy curves and permanent electric dipole moments of 24 electronic states were calculated. In addition we computed the transition dipole moments for transitions from the ground into excited states. The combination of experiment and theory allowed the assignment of features in the recorded spectrum to the excited [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] states, where the experiment allowed to benchmark the calculation. This is the first experimental work giving insight into the previously unknown RbCa molecule, which offers great prospects in ultracold molecular physics due to its magnetic and electronic dipole moment in the [Formula: see text] ground state.
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11
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Lackner F, Krois G, Buchsteiner T, Pototschnig JV, Ernst WE. Helium-droplet-assisted preparation of cold RbSr molecules. PHYSICAL REVIEW LETTERS 2014; 113:153001. [PMID: 25375707 DOI: 10.1103/physrevlett.113.153001] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Indexed: 06/04/2023]
Abstract
We present a combined experimental and theoretical study of the RbSr molecule. The experimental approach is based on the formation of RbSr molecules on helium nanodroplets. Utilizing two-photon ionization spectroscopy, an excitation spectrum ranging from 11,600 up to 23,000 cm(-1) was recorded. High level ab initio calculations of potential energy curves and transition dipole moments accompany the experiment and facilitate an assignment of transitions. We show that RbSr molecules desorb from the helium droplets upon excitation, which enables dispersed fluorescence spectroscopy of free RbSr. These spectra elucidate X(2)Σ(+) ground and excited state properties. Emission spectra originating from states corresponding to the Rb(5s(2)S) + Sr(5s5p(3)P) asymptote were recorded; spin-orbit coupling was included for the simulation. The results should provide a good basis for achieving the formation of this molecule in cold collisions, thus offering intriguing prospects for ultracold molecular physics.
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Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz, Austria
| | - Günter Krois
- Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz, Austria
| | - Thomas Buchsteiner
- Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz, Austria
| | - Johann V Pototschnig
- Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz, Austria
| | - Wolfgang E Ernst
- Institute of Experimental Physics, TU Graz, Petersgasse 16, A-8010 Graz, Austria
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12
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Krois G, Lackner F, Pototschnig JV, Buchsteiner T, Ernst WE. Characterization of RbSr molecules: spectral analysis on helium droplets. Phys Chem Chem Phys 2014; 16:22373-81. [DOI: 10.1039/c4cp03135k] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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13
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Ratschek M, Pototschnig JV, Hauser AW, Ernst WE. Solvation and spectral line shifts of chromium atoms in helium droplets based on a density functional theory approach. J Phys Chem A 2014; 118:6622-31. [PMID: 24906160 PMCID: PMC4141898 DOI: 10.1021/jp5034036] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
![]()
The
interaction of an electronically excited, single chromium (Cr)
atom with superfluid helium nanodroplets of various size (10 to 2000
helium (He) atoms) is studied with helium density functional theory.
Solvation energies and pseudo-diatomic potential energy surfaces are
determined for Cr in its ground state as well as in the y7P, a5S, and y5P excited states. The necessary
Cr–He pair potentials are calculated by standard methods of
molecular orbital-based electronic structure theory. In its electronic
ground state the Cr atom is found to be fully submerged in the droplet.
A solvation shell structure is derived from fluctuations in the radial
helium density. Electronic excitations of an embedded Cr atom are
simulated by confronting the relaxed helium density (ρHe), obtained for Cr in the ground state, with interaction pair potentials
of excited states. The resulting energy shifts for the transitions
z7P ← a7S, y7P ← a7S, z5P ← a5S, and y5P ← a5S are compared to recent fluorescence and
photoionization experiments.
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Affiliation(s)
- Martin Ratschek
- Institute of Experimental Physics, Graz University of Technology , Petersgasse 16, A-8010 Graz, Austria
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14
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Pototschnig JV, Ratschek M, Hauser AW, Ernst WE. An ab initio study of the CrHe diatomic molecule: the effect of van der Waals distortion on a highly magnetic multi-electron system. Phys Chem Chem Phys 2014; 16:9469-78. [PMID: 24722687 DOI: 10.1039/c4cp00559g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The interaction between He and Cr is investigated by means of post-Hartree-Fock molecular orbital theory. We analyze the influence of the van der Waals forces on the complex electronic structure of the chromium atom, starting with its septet manifold and cover the first few electronically excited states up to 30 000 cm(-1). For the sake of a direct comparison with ongoing experiments on Cr-doped helium nanodroplets we extend our analysis to selected states of the quintet manifold in order to explain a non-radiating relaxation from y (7)P(o) to z (5)P(o).
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Affiliation(s)
- Johann V Pototschnig
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria.
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15
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Krasnokutski SA, Huisken F. Reactivity of Iron Atoms at Low Temperature. J Phys Chem A 2014; 118:2612-7. [DOI: 10.1021/jp5007704] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Serge A. Krasnokutski
- Laboratory
Astrophysics Group
of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Helmholtzweg 3, D-07743 Jena, Germany
| | - Friedrich Huisken
- Laboratory
Astrophysics Group
of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Helmholtzweg 3, D-07743 Jena, Germany
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16
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Krois G, Pototschnig JV, Lackner F, Ernst WE. Spectroscopy of cold LiCa molecules formed on helium nanodroplets. J Phys Chem A 2013; 117:13719-31. [PMID: 24028555 PMCID: PMC3871282 DOI: 10.1021/jp407818k] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/11/2013] [Indexed: 11/30/2022]
Abstract
We report on the formation of mixed alkali-alkaline earth molecules (LiCa) on helium nanodroplets and present a comprehensive experimental and theoretical study of the ground and excited states of LiCa. Resonance enhanced multiphoton ionization time-of-flight (REMPI-TOF) spectroscopy and laser induced fluorescence (LIF) spectroscopy were used for the experimental investigation of LiCa from 15000 to 25500 cm(-1). The 4(2)Σ(+) and 3(2)Π states show a vibrational structure accompanied by distinct phonon wings, which allows us to determine molecular parameters as well as to study the interaction of the molecule with the helium droplet. Higher excited states (4(2)Π, 5(2)Σ(+), 5(2)Π, and 6(2)Σ(+)) are not vibrationally resolved and vibronic transitions start to overlap. The experimental spectrum is well reproduced by high-level ab initio calculations. By using a multireference configuration interaction (MRCI) approach, we calculated the 19 lowest lying potential energy curves (PECs) of the LiCa molecule. On the basis of these calculations, we could identify previously unobserved transitions. Our results demonstrate that the helium droplet isolation approach is a powerful method for the characterization of tailor-made alkali-alkaline earth molecules. In this way, important contributions can be made to the search for optimal pathways toward the creation of ultracold alkali-alkaline earth ground state molecules from the corresponding atomic species. Furthermore, a test for PECs calculated by ab initio methods is provided.
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Affiliation(s)
- Günter Krois
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria
| | - Johann V. Pototschnig
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria
| | - Florian Lackner
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria
| | - Wolfgang E. Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria
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17
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Yang S, Ellis AM, Spence D, Feng C, Boatwright A, Latimer E, Binns C. Growing metal nanoparticles in superfluid helium. NANOSCALE 2013; 5:11545-11553. [PMID: 24107922 DOI: 10.1039/c3nr04003h] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
Helium droplets provide a cold and confined environment where atomic and/or molecular dopants can aggregate into clusters and nanoparticles. In particular, the sequential addition of different materials to helium droplets can lead to the formation of a wide range of nanoparticles, including core-shell nanoparticles, which can then be deposited onto a surface. Here we briefly discuss the fundamental properties of helium droplets and then address their implications for the formation of clusters and nanoparticles. Several key experiments on atomic and molecular clusters will be highlighted and new results obtained for nanoparticles formed in this way will be presented. Finally, the versatility, the limitations and new possibilities provided by superfluid helium droplets in nanoscience and nanotechnology will be addressed.
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Affiliation(s)
- Shengfu Yang
- Department of Chemistry, University of Leicester, Leicester LE1 7RH, UK.
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18
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Lackner F, Poms J, Krois G, Pototschnig JV, Ernst WE. Spectroscopy of lithium atoms and molecules on helium nanodroplets. J Phys Chem A 2013; 117:11866-73. [PMID: 23895106 PMCID: PMC3839407 DOI: 10.1021/jp4030238] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
We
report on the spectroscopic investigation of lithium atoms and
lithium dimers in their triplet manifold on the surface of helium
nanodroplets (HeN). We present the excitation spectrum
of the 3p ← 2s and 3d ← 2s two-photon transitions for
single Li atoms on HeN. The atoms are excited from the
2S(Σ) ground state into Δ, Π, and Σ pseudodiatomic
molecular substates. Excitation spectra are recorded by resonance
enhanced multiphoton ionization time-of-flight (REMPI-TOF) mass spectroscopy,
which allows an investigation of the exciplex (Li*–Hem, m = 1–3) formation process
in the Li–HeN system. Electronic states are shifted
and broadened with respect to free atom states, which is explained
within the pseudodiatomic model. The assignment is assisted by theoretical
calculations, which are based on the Orsay–Trento density functional
where the interaction between the helium droplet and the lithium atom
is introduced by a pairwise additive approach. When a droplet is doped
with more than one alkali atom, the fragility of the alkali–HeN systems leads preferably to the formation of high-spin molecules
on the droplets. We use this property of helium nanodroplets for the
preparation of Li dimers in their triplet ground state (13Σu+).
The excitation spectrum of the 23Πg(ν′
= 0–11) ← 13Σu+(ν″ = 0) transition is presented.
The interaction between the molecule and the droplet manifests in
a broadening of the transitions with a characteristic asymmetric form.
The broadening extends to the blue side of each vibronic level, which
is caused by the simultaneous excitation of the molecule and vibrations
of the droplet (phonons). The two isotopes of Li form 6Li2 and 7Li2 as well as isotope
mixed 6Li7Li molecules on the droplet surface.
By using REMPI-TOF mass spectroscopy, isotope-dependent effects could
be studied.
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Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics, Graz University of Technology , Petersgasse 16, A-8010 Graz, Austria/EU
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Lackner F, Krois G, Ernst WE. Rydberg–Ritz analysis and quantum defects for Rb and Cs atoms on helium nanodroplets. Mol Phys 2013. [DOI: 10.1080/00268976.2013.788792] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics, Graz University of Technology , Graz, Austria
| | - Günter Krois
- Institute of Experimental Physics, Graz University of Technology , Graz, Austria
| | - Wolfgang E. Ernst
- Institute of Experimental Physics, Graz University of Technology , Graz, Austria
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Lackner F, Krois G, Koch M, Ernst WE. Rubidium on Helium Droplets: Analysis of an Exotic Rydberg Complex for n* < 20 and 0 ≤ l ≤ 3. J Phys Chem Lett 2012; 3:1404-1408. [PMID: 26286790 DOI: 10.1021/jz300381y] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Rubidium atom Rydberg states perturbed by helium droplets of different sizes provide insight into the role of a nanosized dielectric on the Coulomb potential. The observation of droplet size-dependent shifts of excited states with respect to bare atom states is explained by a decreased quantum defect and a lowered ionization threshold. Within the scope of a Rydberg model, we demonstrate that quantum defects and ionization potentials are constant for each specific Rydberg series, which confirms the Rydberg character of excited Rubidium states on helium droplets. A set of six Rydberg series could be identified. Individual Rydberg states are observed with effective principal quantum numbers up to n* ≈ 19 and l ≤ 3, for which the expectation value of the electron orbital radius is about 10 times larger than the droplet radius.
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Affiliation(s)
- Florian Lackner
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria/EU
| | - Günter Krois
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria/EU
| | - Markus Koch
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria/EU
| | - Wolfgang E Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria/EU
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Poms J, Hauser AW, Ernst WE. Helium nanodroplets doped with xenon and rubidium atoms: a case study of van der Waals interactions between heliophilic and heliophobic dopants. Phys Chem Chem Phys 2012; 14:15158-65. [DOI: 10.1039/c2cp42333b] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Giese C, Stienkemeier F, Mudrich M, Hauser AW, Ernst WE. Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part II. Femtosecond spectroscopy and spectra assignments. Phys Chem Chem Phys 2011; 13:18769-80. [PMID: 21869967 DOI: 10.1039/c1cp21191a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Homo- and heteronuclear alkali quartet trimers of type K(3-n)Rb(n) (n = 0,1,2,3) formed on helium nanodroplets are probed by one-color femtosecond (fs) photoionization (PI) spectroscopy. The obtained frequencies are assigned to vibrations in different electronic states in comparison to high level ab initio calculations of the involved potentials including pronounced Jahn-Teller and spin-orbit couplings. Despite the fact that the resulting complex vibronic structure of the heavy alkali molecules complicates the comparison of experiment and theory we find good agreement for many of the observed lines for all species.
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Affiliation(s)
- Christian Giese
- Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany.
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Lackner F, Krois G, Theisen M, Koch M, Ernst WE. Spectroscopy of nS, nP, and nD Rydberg series of Cs atoms on helium nanodroplets. Phys Chem Chem Phys 2011; 13:18781-8. [PMID: 21789302 DOI: 10.1039/c1cp21280j] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Affiliation(s)
- F Lackner
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, A-8010 Graz, Austria.
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Hauser AW, Ernst WE. Homo- and heteronuclear alkali metal trimers formed on helium nanodroplets. Part I. Vibronic spectra simulations based on ab initio calculations. Phys Chem Chem Phys 2011; 13:18762-8. [DOI: 10.1039/c1cp21163c] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Pifrader A, Allard O, Auböck G, Callegari C, Ernst WE, Huber R, Ancilotto F. One- and two-photon spectroscopy of highly excited states of alkali-metal atoms on helium nanodroplets. J Chem Phys 2010; 133:164502. [DOI: 10.1063/1.3500397] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Ab-initio calculation of the ground and excited states of MgH using a pseudopotential approach. Chem Phys Lett 2009. [DOI: 10.1016/j.cplett.2009.01.078] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Auböck G, Nagl J, Callegari C, Ernst WE. Observation of relativistic E⊗e vibronic coupling in Rb3 and K3 quartet states on helium droplets. J Chem Phys 2008; 129:114501. [DOI: 10.1063/1.2976765] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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