Laser fluorescence detection of nascent product state distributions in reactions of Sc and Y with O2, NO, and SO2

Imaging Rovibrational Excitation of Scattered YO Molecules in Inelastic Collisions with Kr and Ne

Energy transfer between atoms and molecules is fundamental to many physical and chemical processes, and understanding the mechanisms and outcomes of energy transfer is crucial for various applications in physics and chemistry. Here, the rovibrational excitation of YO(X 2Σ+) molecules with the collision of Kr and Ne has been studied in the laser-ablation crossed beam and time-sliced ion velocity map imaging setup in combination with the resonance enhanced multiphoton ionization scheme. Significant changes in the angular distribution for different rovibrational excitations of YO molecules are observed with the collision of Kr. The sharp forward distribution for low rovibrational excitation of YO(v' = 0, 1) molecules suggest that the weak attractive potential between Kr and YO is dominant at large impact parameters. Comparatively, the strong sideway distribution for highly rovibrationally excited YO(v' = 1, 2, 3, and 5) is due to rainbow scattering from the stronger attractive potential of Kr···YO at relatively small impact parameters. The more isotropic angular distribution in the highly rovibrationally excited YO(v' = 11) indicates the formation of a short-lived complex. A change in the angular distribution of scattered YO with different rovibrational excitations was also observed in the collisions of Ne. For YO as a heteronuclear diatomic molecule, collisions of the Y- and the O-end of YO with rare gases would affect the contribution of inelastic processes at different impact parameters.

A full configuration interaction quantum Monte Carlo study of ScO, TiO, and VO molecules

Accurate ab initio calculations of 3d transition metal monoxide molecules have attracted extensive attention because of their relevance in physical and chemical science as well as theoretical challenges in treating strong electron correlation. Meanwhile, recent years have witnessed the rapid development of the full configuration interaction quantum Monte Carlo (FCIQMC) method to tackle electron correlation. In this study, we carry out FCIQMC simulations to ScO, TiO, and VO molecules and obtain accurate descriptions of 13 low-lying electronic states (ScO ²Σ⁺, ²Δ, ²Π; TiO ³Δ, ¹Δ, ¹Σ⁺, ³Π, ³Φ; VO ⁴Σ^-, ⁴Φ, ⁴Π, ²Γ, ²Δ), including states that have significant multi-configurational character. The FCIQMC results are used to assess the performance of several other wave function theory and density functional theory methods. Our study highlights the challenging nature of the electronic structure of transition metal oxides and demonstrates FCIQMC as a promising technique going forward to treat more complex transition metal oxide molecules and materials.

Towards accurate prediction for laser-coolable molecules: relativistic coupled-cluster calculations for yttrium monoxide and prospects for improving its laser cooling efficiencies

Benchmark relativistic coupled-cluster calculations for yttrium monoxide (YO) with accurate treatment of relativistic and electron correlation effects are reported. The spin-orbit mixing of 2Π and 2Δ is found to be an order of magnitude smaller than previously reported in the literature. Together with the measurement of the lifetime of the A'2Δ3/2 state, it implies an enhanced capability of a narrow-line cooling scheme to bring YO to sub-recoil temperature. The computed electronic transition properties also support a four-photon scheme to close the leakage of the A2Π1/2 ↔ X2Σ1/2+ cycle through the A'2Δ3/2 state by repumping the A'2Δ3/2 state to the B2Σ1/2+ state, which subsequently decays back to X2Σ1/2+. Relativistic coupled-cluster methods, capable of providing accurate spectroscopic parameters that characterize the local potential curves and hence of providing accurate Franck-Condon factors, appear to be promising candidates for accurate calculation of properties for laser-coolable molecules.

Sub-Doppler Cooling and Compressed Trapping of YO Molecules at μK Temperatures

Complex molecular structure demands customized solutions to laser cooling by extending its general set of principles and practices. Compared with other laser-cooled molecules, yttrium monoxide (YO) exhibits a large electron-nucleus interaction, resulting in a dominant hyperfine interaction over the electron spin-rotation coupling. The YO ground state is thus comprised of two manifolds of closely spaced states, with one of them possessing a negligible Landé g factor. This unique energy level structure favors dual-frequency dc magneto-optical trapping (MOT) and gray molasses cooling (GMC). We report exceptionally robust cooling of YO at 4 μK over a wide range of laser intensity, detunings (one- and two-photon), and magnetic field. The magnetic insensitivity enables the spatial compression of the molecular cloud by alternating GMC and MOT under the continuous operation of the quadrupole magnetic field. A combination of these techniques produces a laser-cooled molecular sample with the highest phase space density in free space.

Spectroscopy of YO from first principles

We report an ab initio study on the spectroscopy of the open-shell diatomic molecule yttrium oxide, YO. The study considers the six lowest doublet states, X2Σ+, A'2Δ, A2Π, B2Σ+, C2Π, D2Σ+, and a few higher-lying quartet states using high levels of electronic structure theory and accurate nuclear motion calculations. The coupled cluster singles, doubles, and perturbative triples, CCSD(T), and multireference configuration interaction (MRCI) methods are employed in conjunction with a relativistic pseudopotential on the yttrium atom and a series of correlation-consistent basis sets ranging in size from triple-ζ to quintuple-ζ quality. Core-valence correlation effects are taken into account and complete basis set limit extrapolation is performed for CCSD(T). Spin-orbit coupling is included through the use of both MRCI state-interaction with spin-orbit (SI-SO) approach and four-component relativistic equation-of-motion CCSD calculations. Using the ab initio data for bond lengths ranging from 1.0 to 2.5 Å, we compute 6 potential energy, 12 spin-orbit, 8 electronic angular momentum, 6 electric dipole moment and 12 transition dipole moment (4 parallel and 8 perpendicular) curves which provide a complete description of the spectroscopy of the system of six lowest doublet states. The Duo nuclear motion program is used to solve the coupled nuclear motion Schrödinger equation for these six electronic states. The spectra of 89Y16O simulated for different temperatures are compared with several available high resolution experimental studies; good agreement is found once minor adjustments are made to the electronic excitation energies.

2D Magneto-optical trapping of diatomic molecules

We demonstrate one- and two-dimensional transverse laser cooling and magneto-optical trapping of the polar molecule yttrium (II) oxide (YO). In a 1D magneto-optical trap (MOT), we characterize the magneto-optical trapping force and decrease the transverse temperature by an order of magnitude, from 25 to 2 mK, limited by interaction time. In a 2D MOT, we enhance the intensity of the YO beam and reduce the transverse temperature in both transverse directions. The approach demonstrated here can be applied to many molecular species and can also be extended to 3D.

First-principles calculations of the electronic and geometrical structures of neutral [Sc,O,H] molecules and the monocations, ScOH(0,+) and HScO(0,+)

Using multireference configuration interaction and coupled-cluster methodologies, with quadruple-ζ basis sets, we explored the potential energy surfaces of the ground and excited states of the neutral and cationic triatomics [Sc,O,H](0,+). In its ground state, the neutral species is trapped into either a linear ScOH or a bent HScO conformation; these two minima are approximately equal in energy and separated by a barrier of 40 kcal/mol. The linear ScOH structure is preferred by the excited states of the neutral species and by all of the electronic states of the charged molecular systems that we studied in this work. Both ScOH and ScOH(+) present ionic characters, Sc(+)OH(-) and Sc(2+)OH(-), similar to those found for the isovalent ScF(0,+) species. The HScO(0,+) structures are obtained by covalent or dative interaction of hydrogen and ScO(0,+). For most of the minima located in this work, we calculated geometries, vibrational frequencies, binding energies, excitation energies, and dipole moments. Our numerical results agree well with existing experimental data.

Excited state reaction dynamics of Ti(a(5)F(J)) + O2 --> TiO(A,B) + O studied by a crossed-beam technique

Oxidation reactions of the gas-phase titanium atom in its excited state with oxygen molecule, Ti(a(5)F(J)) + O(2) --> TiO(A(3)Phi,B(3)Pi) + O, were studied by a crossed-beam technique. Metastable excited Ti, Ti(a(5)F(J)), was generated by an optical pumping method and the reaction products were detected by the chemiluminescence spectroscopy. The chemiluminescence from TiO(A(3)Phi,B(3)Pi) was analyzed to determine vib-rotational state distributions of both excited states and their branching ratio. The vib-rotational state distribution of TiO(B) was represented by the statistical energy disposal and the branching ratio of TiO(A)/TiO(B) was also consistent with the statistical expectation. These results suggested the presence of long-lived intermediates in the course of the reactions of the excited Ti(a(5)F(J)) atom with O(2). Also observed was the significant deviation of the vibrational state distribution of TiO(A) from the statistical one and another reaction pathway which may not proceed via the long-lived intermediates was implied.

Reaction dynamics of V(aFJ4)+NO→VO(XΣ−4)+N studied by a crossed-beam laser-induced fluorescence technique

The dynamics of the reaction, V(a 4FJ)+NO-->VO(X 4Sigma-)+N was studied by using a crossed-beam technique at 16.4 kJ/mol of collision energy. The V atomic beam was generated by laser vaporization and crossed with the O2 beam at a right angle. The laser-induced fluorescence (LIF) for the transition of VO(B 4Pi-X 4Sigma) was used to determine the rotational state distribution of the reaction product in the vibrational ground state. Almost pure V(a 4FJ) beam was obtained by using the mixture of NH3 with N2 as a carrier gas. Comparing the LIF spectra of VO measured for two carrier gases, i.e., NH3N2 and pure N2, it was concluded that the vibrational ground state of VO(X 4Sigma-) is formed almost entirely from the reaction of V(a 4FJ) and the contribution of the metastable V(a 6DJ) is negligible. The observed rotational distribution was similar to a statistical prior prediction, and suggested that the title reaction proceeds via a long-lived intermediate, which is consistent with an electron transfer mechanism.

Reaction dynamics of Y + O2→ YO(X,A′,A)+ O(3PJ) studied by the crossed-beam technique

The dynamics of the reaction, Y + O2--> YO + O was studied by using the crossed-beam technique at several collision energies from 10.3 to 52.0 kJ mol(-1). The Y atomic beam was generated by laser vaporization and crossed with the O2 beam at a right angle. Among the energetically accessible electronic states of YO, the formation of the A2Pi and A'2Delta states was observed by their chemiluminescence at all collision energies. By analyzing the chemiluminescence spectra of YO(A2Pi(1/2,3/2)-X2Sigma+), vibrational state distributions and relative populations of spin-orbit states were determined for YO(A2Pi(1/2,3/2)). At low collision energies, the vibrational distributions agree quite well with those expected from the statistical energy partitioning, while a little deviation from the statistical expectation was observed at the highest energy, 52.0 kJ mol(-1). The populations of two spin-orbit states are in good agreement with the statistical expectations at all collision energies. The vacuum ultraviolet laser-induced fluorescence (VUV-LIF) technique was employed to determine the distributions of spin-orbit states of the product O(3P(J)) at two collision energies, 20.7 and 52.0 kJ mol(-1). The line shapes of the O atom transitions were analyzed to determine relative branching ratio of the ground state to the excited states of YO, i.e. YO(X2Sigma+)+ O(3P(J))vs. YO(A2Pi and A'2Delta)+ O(3P(J)). The results showed that the electronically excited YO was formed with comparable amount with the ground state which is statistically more favorable, and suggested the occurrence of two mechanisms taking place in the title reaction.