New Developments in Matrix Isolation Spectroscopy

Experimental perspectives on the matter-antimatter asymmetry puzzle: developments in electron EDM and [Formula: see text] experiments

In the search for clues to the matter-antimatter puzzle, experiments with atoms or molecules play a particular role. These systems allow measurements with very high precision, as demonstrated by the unprecedented limits down to [Formula: see text] e cm on electron EDM using molecular ions, and relative measurements at the level of [Formula: see text] in spectroscopy of antihydrogen atoms. Building on these impressive measurements, new experimental directions offer potential for drastic improvements. We review here some of the new perspectives in those fields and their associated prospects for new physics searches. This article is part of the theme issue 'The particle-gravity frontier'.

Matrix effects in MI-VCD spectra of two chiral oxiranes and their potential microscopic origin

Combining vibrational circular dichroism (VCD) spectroscopy with the matrix isolation (MI) technique opens up interesting possibilities to study chiral molecules. MI involves the isolation of guest species in inert solid matrices at cryogenic temperatures. Hence, MI-VCD measures are solid-state VCD measurements, and as such, can suffer from mostly birefringance-related artefacts in the same way as common solid-state VCD measurements. In this contribution, we demonstrate that the sample preparation condition have tremendous impact on the quality and reliability of the recorded MI-VCD spectra. While MI-IR spectra are basically blind to these artefacts, the variation of deposition temperatures and host flow rates seem to control whether high quality MI-VCD spectra are obtained or if depolarization effects lead to completely obscured spectra. For two selected examples, styrene oxide (SO) and 1-phenyl propylene oxide (PPO), we discuss how the various experimental conditions may lead to the aforementioned effects and give a microscopic description of their origin.

On-Surface Synthesis and Real-Space Visualization of Aromatic P3 N3

On-surface synthesis is at the verge of emerging as the method of choice for the generation and visualization of unstable or unconventional molecules, which could not be obtained via traditional synthetic methods. A case in point is the on-surface synthesis of the structurally elusive cyclotriphosphazene (P3 N3 ), an inorganic aromatic analogue of benzene. Here, we report the preparation of this fleetingly existing species on Cu(111) and Au(111) surfaces at 5.2 K through molecular manipulation with unprecedented precision, i.e., voltage pulse-induced sextuple dechlorination of an ultra-small (about 6 Å) hexachlorophosphazene P3 N3 Cl6 precursor by the tip of a scanning probe microscope. Real-space atomic-level imaging of cyclotriphosphazene reveals its planar D3h -symmetric ring structure. Furthermore, this demasking strategy has been expanded to generate cyclotriphosphazene from a hexaazide precursor P3 N21 via a different stimulation method (photolysis) for complementary measurements by matrix isolation infrared and ultraviolet spectroscopy.

Photoelectron Photoion Coincidence Spectroscopy of Biradicals

The electronic structure of biradicals is characterized by the presence of two unpaired electrons in degenerate or near-degenerate molecular orbitals. In particular, some of the most relevant species are highly reactive, difficult to generate cleanly and can only be studied in the gas phase or in matrices. Unveiling their electronic structure is, however, of paramount interest to understand their chemistry. Photoelectron photoion coincidence (PEPICO) spectroscopy is an excellent approach to explore the electronic states of biradicals, because it enables a direct correlation between the detected ions and electrons. This permits to extract unique vibrationally resolved photoion mass-selected threshold photoelectron spectra (ms-TPES) to obtain insight in the electronic structure of both the neutral and the cation. In this review we highlight most recent advances on the spectroscopy of biradicals and biradicaloids, utilizing PEPICO spectroscopy and vacuum ultraviolet (VUV) synchrotron radiation.

Pyridine Dimers and Their Low-Temperature Isomerization: A High-Resolution Matrix-Isolation Spectroscopy Study

The bonding between two neutral aromatic compounds, especially small ones, has been controversially debated in the last decades, and terms like "π-stacking" had to be revised. Surprisingly, despite of many experimental and computational work, there is still no clear consensus about the structure of and the bonding in the pyridine dimer. In this work, for different isomeric forms of the pyridine dimer, the structures and bonding were elucidated by combining high-resolution matrix-isolation spectroscopic results with quantum-chemical calculations. High-resolution IR spectra of Ne matrices at 4 K containing pyridine were recorded for different concentrations and upon annealing to 10 and 12 K, relying on three isotopologues of pyridine. The spectra show the presence of hydrogen-bonded, T-shaped, and stacked forms of weakly-bound pyridine dimers. Among these, the hydrogen-bonded isomer is identified as the lowest-energy form. The results provide for the first time conclusive information about the interaction between two pyridine dimers.

UV Laser-Induced Phototransformations of Matrix-Isolated 5-Chloro-3-nitro-2-hydroxyacetophenone

Conformational changes of 5-chloro-3-nitro-2-hydroxyacetophenone were studied by experimental and theoretical methods. Phototransformations of the compound were induced in low-temperature argon matrices by using UV radiation, which was followed by FT-IR measurements. Two types of changes within the molecule were detected: rotations of the hydroxyl and acetyl groups. A new conformer without an intramolecular hydrogen bond was generated upon irradiation with λ = 330 nm, whereas the reverse reaction was observed at 415 nm.

On the vibrations of formic acid predicted from first principles

In this article, we review recent first principles, anharmonic studies on the molecular vibrations of gaseous formic acid in its monomer form. Transitions identified as fundamentals for both cis- and trans form reported in these studies are collected and supported by results from high-resolution experiments. Attention is given to the effect of coordinate coupling on the convergence of the computed vibrational states.

Neural network interaction potentials for para-hydrogen with flexible molecules

The study of molecular impurities in para-hydrogen ( pH2) clusters is key to push forward our understanding of intra- and intermolecular interactions, including their impact on the superfluid response of this bosonic quantum solvent. This includes tagging with only one or very few pH2, the microsolvation regime for intermediate particle numbers, and matrix isolation with many solvent molecules. However, the fundamental coupling between the bosonic pH2 environment and the (ro-)vibrational motion of molecular impurities remains poorly understood. Quantum simulations can, in principle, provide the necessary atomistic insight, but they require very accurate descriptions of the involved interactions. Here, we present a data-driven approach for the generation of impurity⋯ pH2 interaction potentials based on machine learning techniques, which retain the full flexibility of the dopant species. We employ the well-established adiabatic hindered rotor (AHR) averaging technique to include the impact of the nuclear spin statistics on the symmetry-allowed rotational quantum numbers of pH2. Embedding this averaging procedure within the high-dimensional neural network potential (NNP) framework enables the generation of highly accurate AHR-averaged NNPs at coupled cluster accuracy, namely, explicitly correlated coupled cluster single, double, and scaled perturbative triples, CCSD(T*)-F12a/aVTZcp, in an automated manner. We apply this methodology to the water and protonated water molecules as representative cases for quasi-rigid and highly flexible molecules, respectively, and obtain AHR-averaged NNPs that reliably describe the corresponding H2O⋯ pH2 and H3O+⋯ pH2 interactions. Using path integral simulations, we show for the hydronium cation, H3O+, that umbrella-like tunneling inversion has a strong impact on the first and second pH2 microsolvation shells. The automated and data-driven nature of our protocol opens the door to the study of bosonic pH2 quantum solvation for a wide range of embedded impurities.

Spectroscopy of Alkali Atoms in Solid Matrices of Rare Gases: Experimental Results and Theoretical Analysis

We present an experimental and theoretical investigation of the spectroscopy of dilute alkali atoms in a solid matrix of inert gases at cryogenic temperatures, specifically Rubidium atoms in a solid Argon or Neon matrix, and related aspects of the interaction energies between the alkali atoms and the atoms of the solid matrix. The system considered is relevant for matrix isolation spectroscopy, and it is at the basis of a recently proposed detector of cosmological axions, exploiting magnetic-type transitions between Zeeman sublevels of alkali atoms in a magnetic field, tuned to the axion mass, assumed in the meV range. Axions are one of the supposed constituents of the dark matter (DM) of the Universe. This kind of spectroscopy could be also relevant for the experimental search of new physics beyond the Standard Model, in particular the search of violations of time-reversal or parity-charge-conjugation (CP) symmetry. In order to efficiently resolve the axion-induced transition in alkali-doped solid matrices, it is necessary to reduce as much as possible the spectral linewidth of the electronic transitions involved. The theoretical investigation presented in this paper aims to estimate the order of magnitude of the inhomogeneous contribution to the linewidth due to the alkali–matrix interactions (Coulomb/exchange and dispersion), and to compare the theoretical results with our experimental measurements of spectra of dilute Rubidium atoms in Argon and Neon solid matrix. The comparison of the expected or measured spectral linewidths will be important for selecting the most appropriate combination of alkali atoms and matrix inert elements to be used in the proposed axion detection scheme. It is finally suggested that dilute Lithium atoms diffused in a cold parahydrogen solid matrix could be, overall, a good system upon which the proposed detector could be based.

Toward size-dependent thermodynamics of nanoparticles from quantum chemical calculations of small atomic clusters: a case study of (B2O3)n

We present a method for obtaining canonical partition functions and, accordingly, temperature-dependent thermodynamics of arbitrary-sized (nano) particles from electronic structure calculations of the corresponding small size atomic clusters. The guiding idea here is to extrapolate the basic properties underlying the thermochemistry of clusters (electronic energies, rotational constants, and vibrational frequencies) rather than the thermodynamic functions themselves. The thus obtained scaling dependences for these basic properties expressed in a simple analytical form provide an efficient tool for fast evaluation of the size-selected thermochemical data for particles of any nuclearity. To exemplify the performance of the methodology, neutral stoichiometric boron oxide clusters are considered. To this end, the geometry and various physical properties of the energetically lowest-lying (B₂O₃)_n (n = 1,…,8) structures are found using density functional theory and the authors' multistage hierarchical procedure customized for global optimization of quite large cluster structures. With these data and based on the physically consistent scaling regularities for the principal cluster properties, the size-selected thermodynamic functions of boron oxide particles in the gas phase, such as enthalpy, entropy, and specific heat capacity, are derived. The variation of these characteristics with increasing cluster size is discussed in detail as well. To facilitate handling of the temperature and size dependences we have found here in further chemical kinetic and equilibrium modeling, the tabulated thermodynamic functions of interest are fitted for n = 1,…,1000 to the standard seven-parameter Chemkin polynomials.

Weakly Bound Complex Formation between HCN and CH3Cl: A Matrix-Isolation and Computational Study

The matrix-isolated infrared spectrum of a hydrogen cyanide-methyl chloride complex was investigated in a solid argon matrix. HCN and CH₃Cl were co-condensed onto a substrate held at 10 K with an excess of argon gas, and the infrared spectrum was measured using Fourier-transform infrared spectroscopy. Quantum chemical geometry optimization, harmonic frequency, and natural bonding orbital calculations indicate stabilized hydrogen- and halogen-bonded structures. The two resulting weakly bound complexes are both composed of one CH₃Cl molecule bound to a (HCN)₃ subunit, where the three HCN molecules are bound head-to-tail in a ring formation. Our study suggests that─in the presence of CH₃Cl─the formation of (HCN)₃ is promoted through complexation. Since HCN aggregates are an important precursor to prebiotic monomers (amino acids and nucleobases) and other life-bearing polymers, this study has astrophysical implications toward the search for life in space.

Formation and Evolution of H2C3O+• Radical Cations: A Computational and Matrix Isolation Study

The family of isomeric H₂C₃O^+• radical cations is of great interest for physical organic chemistry and chemistry occurring in extraterrestrial media. In this work, we have experimentally examined a unique synthetic route to the generation of H₂C₃O^+• from the C₂H₂···CO intermolecular complex and also considered the relative stability and monomolecular transformations of the H₂C₃O^+• isomers through high-level ab initio calculations. The structures, energetics, harmonic frequencies, hyperfine coupling constants, and isomerization pathways for several of the most important H₂C₃O^+• isomers were calculated at the UCCSD(T) level of theory. The complementary FTIR and EPR studies in argon matrices at 5 K have demonstrated that the ionized C₂H₂···CO complex transforms into the E-HCCHCO^+• isomer, and this latter species is supposed to be the key intermediate in further chemical transformations, providing a remarkable piece of evidence for kinetic control in low-temperature chemistry. Photolysis of this species at λ = 410-465 nm results in its transformation to the thermodynamically most stable H₂CCCO^+• isomer. Possible implications of the results and potentiality of the proposed synthetic strategy to the preparation of highly reactive organic radical cations are discussed.

An Organic Capsule as a Matrix to Capture and Store Reactive Molecules at Room Temperature in Aqueous Solution: 7-cis-β-Ionone†

Low-temperature m atrix isolation method is the most popular one to generate and store reactive molecules and characterize them by in situ IR spectroscopy. Recognizing the need for a simpler method to trap and store such molecules and characterize by NMR spectroscopy at room temperature in solution, we have performed experiments exploring the value of water-soluble octa acid (OA) capsule as a storage vessel. The molecule we have chosen to illustrate the feasibility is the highly hindered 7-cis-β-ionone, which has been established to exist in equilibrium with its cyclic form with the later favored at room temperature. In this study, we have shown that confined space can be an alternative to temperature to tilt an equilibrium toward higher energy isomer. During the course of the study, we were surprised to note that 7-trans-β-ionone aggregates in water and has distinct ¹ H NMR spectra. Ability to assemble characterizable organic aggregates in water reveals the value of water as a reaction medium that is yet to be fully explored by photochemists. Finally, we have clarified the likely mechanism of secondary photoreaction of α-pyran to the final photoproduct that involves 1,5-hydrogen migration.

Beryllium Atom Mediated Dinitrogen Activation via Coupling with Carbon Monoxide

The reactions of laser-ablated beryllium atoms with dinitrogen and carbon monoxide mixtures form the end-on bonded NNBeCO and side-on bonded (η2 -N2 )BeCO isomers in solid argon, which are predicted by quantum chemical calculations to be almost isoenergetic. The end-on bonded complex has a triplet ground state while the side-on bonded isomer has a singlet electronic ground state. The complexes rearrange to the energetically lowest lying NBeNCO isomer upon visible light excitation, which is characterized to be an isocyanate complex of a nitrene derivative with a triplet electronic ground state. A bonding analysis using a charge- and energy decomposition procedure reveals that the electronic reference state of Be in the NNBeCO isomers has an 2s0 2p2 excited configuration and that the metal-ligand bonds can be described in terms of N2 →Be←CO σ donation and concomitant N2 ←Be→CO π backdonation. The results demonstrate that the activation of N2 with the N-N bond being completely cleaved can be achieved via coupling with carbon monoxide mediated by a main group atom.

Considerable matrix shift in the electronic transitions of helium-solvated cesium dimer cation Cs2He

We investigate the photodissociation of helium-solvated cesium dimer cations using action spectroscopy and quantum chemical calculations. The spectrum of Cs2He+ shows three distinct absorption bands into both bound and dissociative states. Upon solvation with further helium atoms, considerable shifts of the absorption bands are observed, exceeding 0.1 eV (850 cm-1) already for Cs2He10+, along with significant broadening. The shifts are highly sensitive to the character of the excited state. Our calculations show that helium atoms adsorb on the ends of Cs2+. The shifts are particularly pronounced if the excited state orbitals extend to the area occupied by the helium atoms. In this case, Pauli repulsion leads to a deformation of the excited state orbitals, resulting in the observed blue shift of the transition. Since the position of the weakly bound helium atoms is ill defined, Pauli repulsion also explains the broadening.

Stable axially symmetric atomic impurity in an fcc solid-Ba in rare gases

Closed-shell metal atoms in rare gas solids tend to occupy highly symmetric polyhedral crystal sites, as follows from the generic triplet Jahn-Teller splitting of the S → P excitation bands and complies with the isotropic nature of the dispersion forces. Atypical 2 + 1 Jahn-Teller splitting inherent to axially symmetric sites observed recently for Ba atoms has been therefore interpreted as the defect accommodation. By modeling the structure, stability, and spectra of the Ba atom in the face-centered cubic rare gas crystals, we identify thermodynamically stable crystal site of axial C_3v symmetry that explains experimental observations. We also demonstrate the dramatic effect of the interaction anisotropy on the trapping site structure and stability for an excited P-state atom. Our results provide strong evidence for stable axially symmetric accommodation of isotropic impurity in a close-packed lattice.

Extraterrestrial prebiotic molecules: photochemistryvs.radiation chemistry of interstellar ices

Photochemistry and radiation chemistry of interstellar ices lead to the synthesis of prebiotic molecules which may be delivered to planets by meteorites and/or comets.

UV-Vis, Fluorescence, and Resonance Raman Spectroscopic and Density Functional Theoretical Studies on 3-Amino-1,2,4-triazole: Microsolvation and Solvent-Dependent Nonadiabatic Excited State Decay in Solution

The microsolvation and photophysics of 3-amino-1,2,4-triazole (3AT) after excitation to the light-absorbing S₂(nπ*) state were studied by using resonance Raman spectroscopy and single component artificial force-induced reaction (SC-AFIR) in a global reaction route mapping (GRRM) strategy. The vibrational spectra were assigned on the basis of experimental data and density functional theory (DFT) calculations. The resonance Raman spectra of 3AT were measured to probe the excited state structural dynamics in the Franck-Condon region. The conformations of 3AT(CH₃CN)₁, 3AT(CH₃OH)₂, and 3AT(H₂O)₂ clusters were determined by combining vibrational spectrum experiments and B3LYP/6-311++G(d,p) computations. DFT calculations were carried out to obtain the minimal excitation energies of the lower-lying singlet excited states, and the curve-crossing points. It was revealed that the short-time structural dynamics of 3AT were dominated by the N-N stretching coordinates. An excited state decay mechanism is proposed: 3AT is initially excited to the S₂(nπ*) state, then the conical intersection (CI) of the S₂(nπ*)/S₁(ππ*) potential energy surfaces is crossed, and 3AT then decays to the lower solvent-dependent excited state S₁(ππ*). It subsequently returns to the S₀ state, accompanied by a large Stokes fluorescence shift, which was interpreted as the stabilized S₁(ππ*) excited state bonding to several water molecules via intermolecular hydrogen bonding.

Development of an experimental set-up for low-temperature spectroscopic studies of matrix-isolated molecules and molecular ices using synchrotron radiation

An experimental set-up for studying photophysics and photochemistry of molecules in an inert gas medium (matrix-isolated) and in the ice phase at low temperatures has been developed and commissioned at the Photophysics beamline, Indus-1 synchrotron radiation source. This end-station uses an in-house-developed closed-cycle cryostat for achieving cryo-temperatures (∼10 K). Synchrotron radiation from the Photophysics beamline is used as the source of UV-VUV photons and the system is equipped with a Fourier transform infrared spectrometer for characterization of the molecular species formed at low temperature. Various individual components of the end-station like closed-cycle cryostat, experimental chamber, gas mixing and deposition systems are tested to ascertain that the desired performance criteria are satisfied. The performance of the composite system after integration with the Photophysics beamline is evaluated by recording IR and UV-VUV photoabsorption spectra of sulfur dioxide at low temperatures (10 K), both in the ice phase as well as isolated in argon matrices. Results obtained are in good agreement with earlier literature, thus validating the satisfactory performance of the system. As an off-shoot of the study, the VUV absorption spectrum of matrix-isolated SO₂ in argon matrix up to 10.2 eV is reported here for the first time. This experimental end-station will provide new opportunities to study photon-induced reactions in molecules of environmental, astrochemical and industrial importance. Details of the design, development and initial experimental results obtained are presented.

Metal Cluster Models for Heterogeneous Catalysis: A Matrix-Isolation Perspective

Metal cluster models are of high relevance for establishing new mechanistic concepts for heterogeneous catalysis. The high reactivity and particular selectivity of metal clusters is caused by the wealth of low-lying electronically excited states that are often thermally populated. Thereby the metal clusters are flexible with regard to their electronic structure and can adjust their states to be appropriate for the reaction with a particular substrate. The matrix isolation technique is ideally suited for studying excited state reactivity. The low matrix temperatures (generally 4-40 K) of the noble gas matrix host guarantee that all clusters are in their electronic ground-state (with only a very few exceptions). Electronically excited states can then be selectively populated and their reactivity probed. Unfortunately, a systematic research in this direction has not been made up to date. The purpose of this review is to provide the grounds for a directed approach to understand cluster reactivity through matrix-isolation studies combined with quantum chemical calculations.

Pentavalent lanthanide nitride-oxides: NPrO and NPrO- complexes with N≡Pr triple bonds

The neutral molecule NPrO and its anion NPrO^- are produced via co-condensation of laser-ablated praseodymium atoms with nitric oxide in a solid neon matrix. Combined infrared spectroscopy and state-of-the-art quantum chemical calculations confirm that both species are pentavalent praseodymium nitride-oxides with linear structures that contain Pr≡N triple bonds and Pr=O double bonds. Electronic structure studies show that the neutral NPrO molecule features a 4f⁰ electron configuration and a Pr(v) oxidation state similar to that of the isoelectronic PrO₂⁺ ion, while its NPrO^- anion possesses a 4f¹ electron configuration and a Pr(iv) oxidation state. The neutral NPrO molecule is thus a rare lanthanide nitride-oxide species with a Pr(v) oxidation state, which follows the recent identification of the first Pr(v) oxidation state in the PrO₂⁺ and PrO₄ complexes (Angew. Chem. Int. Ed., 2016, 55, 6896). This finding indicates that lanthanide compounds with oxidation states of higher than +IV are richer in chemistry than previously recognized.

Observation of Spontaneous C=C Bond Breaking in the Reaction between Atomic Boron and Ethylene in Solid Neon

A ground-state boron atom inserts into the C=C bond of ethylene to spontaneously form the allene-like compound H2 CBCH2 on annealing in solid neon. This compound can further isomerize to the propyne-like HCBCH3 isomer under UV light excitation. The observation of this unique spontaneous C=C bond insertion reaction is consistent with theoretical predictions that the reaction is thermodynamically exothermic and kinetically facile. This work demonstrates that the stronger C=C bond, rather than the less inert C-H bond, can be broken to form organoboron species from the reaction of a boron atom with ethylene even at cryogenic temperatures.

Experimental and theoretical identification of the Fe(vii) oxidation state in FeO4−

Two isomers of iron tetraoxygen anion, dioxoiron peroxide [(η²-O₂)FeO₂]⁻ and tetroxide FeO₄⁻ were characterized by experiment and theoretical calculations, with heptavalent Fe(vii) oxidation state identified in the later.

Identification of diborane(4) with bridging B-H-B bonds

The irradiation of diborane(6) dispersed in solid neon at 3 K with far-ultraviolet light generated diborane(4), B₂H₄, with bridging B–H–B bonds.

The irradiation of diborane(6) dispersed in solid neon at 3 K with tunable far-ultraviolet light from a synchrotron yielded a set of IR absorption lines, the pattern of which implies a carrier containing two boron atoms. According to isotope effects and quantum-chemical calculations, we identified this new species as diborane(4), B₂H₄, possessing two bridging B–H–B bonds. Our work thus establishes a new prototype, diborane(4), for bridging B–H–B bonds in molecular structures.

Low-lying electronic states in bismuth trimer Bi₃ as revealed by laser-induced NIR emission spectroscopy in solid Ne

Laser-induced near-infrared (NIR) emission spectra of neutral bismuth timer, Bi₃, embedded in solid neon matrixes at 3 K were recorded in a range 870-1670 nm. Using photoexcitation with low energy photons at 1064 nm, two emission band systems were newly identified by their origin bands at T₀ = 6600 and 8470 cm⁻¹. Accordingly, spectral assignment for three NIR emission band systems reported recently was partly revised for the one with its origin band at T₀ = 7755 cm⁻¹ and reconfirmed for the others at T₀ = 9625 and 11,395 cm⁻¹. Energy splitting by spin-orbit coupling between the pair of electronic energy levels in the ground state of bismuth trimer, Bi₃, both having a totally symmetric vibrational mode of frequency at ω(e)" = 150 cm⁻¹, was determined to be 1870 ± 1.5 cm⁻¹. Transitions from the pair of electronically excited states, locating at T₀ = 8470 and 9625 cm⁻¹ above the ground state and separated by spin–orbit coupling of 1155 cm⁻¹, have relatively long decay constants of τ ∼0.2 and ∼0.1 ms, respectively.

Study of interaction between NO radicals and Martin's spirosilane by means of IR spectroscopy

The matrix isolation method is used to record the IR spectrum of C18H8O2F12Si in the 4000-500 cm(-1) range. To gain an IR spectrum with a sufficient resolution, this technique was used with neon as the dilution medium at 5 K. The generated species were characterized by in situ fourier transform infrared (FT-IR) spectroscopy. Once the Martin's spirosilane 1 (C18H8O2F12Si) was characterized, its reactivity toward NO was investigated under the same experimental conditions (i.e., using neon as a dilution medium at 5 K). In this case, the use of neon at very low temperature leads to the formation of a chemically inert matrix in which the species are trapped and isolated from one another, thus hindering consecutive reactions. As a consequence, intermediates can be observed. This approach allowed us to characterize the NO adduct, leading to the formation of 1-(NO). Concentration effects as well as annealing experiments were carried out. In addition to this experimental approach, products were identified by using reference spectra. Our results proved that, in the dilute phase, the reaction between 1 and NO radicals leads to the formation of an adduct. This stable species can further react with NO to form a more stable compound: 1-(NO)2. This proves the ability of such species to trap NO.

Structure characterization of metal oxide clusters by vibrational spectroscopy: possibilities and prospects

This article summarizes the methodological progress that has been made in the vibrational spectroscopy of isolated polynuclear metal oxide clusters, with particular emphasis on free electron laser-based infrared action spectroscopy of gas phase clusters, over the last decade. The possibilities, limitations and prospects of the various experimental approaches are discussed using representative examples from pivotal studies in the field.

Optical excitation and decay dynamics of ytterbium atoms embedded in a solid neon matrix

Neutral ytterbium atoms embedded in solid neon qualitatively retain the structure of free atoms. Despite the atom-solid interaction, the 6s6p ³P(0) level is found to remain metastable with its lifetimes determined to be in the range of ten to hundreds of seconds. The atomic population can be almost completely transferred between the ground level and the metastable level via optical excitation and spontaneous decay. The dynamics of this process is examined and is used to explicitly demonstrate that the transition broadening mechanism is homogeneous.

Matrix isolation infrared spectroscopic and theoretical study of the reactions of tantalum oxide molecules with methanol

The reactions of tantalum monoxide (TaO) and dioxide (TaO(2)) molecules with methanol in solid neon were investigated by infrared absorption spectroscopy. The ground-state TaO molecule reacted with CH(3)OH in forming the CH(3)OTa(O)H molecule via the hydroxylic hydrogen atom transfer from methanol to the metal center spontaneously on annealing. The observation of the spontaneous reaction is consistent with theoretical predictions that the OH bond activation process is both thermodynamically exothermic and kinetically facile. In contrast, the TaO(2) molecule reacted with CH(3)OH to give primarily the TaO(2)(CH(3)OH) complex, which further rearranged to the CH(3)OTa(O)OH isomer via the hydroxylic hydrogen atom transfer from methanol to one of oxygen atom of metal dioxide upon visible light excitation.

Reactions of molybdenum and tungsten atoms with nitrous oxide in excess argon: a combined matrix infrared spectroscopic and theoretical study

Reactions of laser-ablated Mo and W atoms with the N(2)O molecules in excess argon have been investigated using matrix-isolation infrared spectroscopy. In the reaction of the N(2)O molecule with the Mo atom, the absorptions at 1960.3 and 934.4 cm(-1) are assigned to the N-N and Mo-O stretching vibrations of the OMoNN complex, respectively. An analogous OWNN complex has also been observed in the W + N(2)O reaction. Infrared spectroscopy also provides evidence for the formation of the OW(NN)(2) complexes. Density functional theory calculations have been performed on the products. Overall agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts supports the identification of these species from the matrix infrared spectra. Furthermore, a plausible reaction mechanism for the formation of these products has been proposed.