The multidimensional nature of classically hindered proton transfer is demonstrated clearly by the pronounced effects engendered by attendant electronic and vibrational degrees of freedom, the selective excitation of which can enhance or diminsh the rate of hydron migration greatly. To explore the provenance of such phenomena, the origin band (0⁰₀) of the ùB₂–~X¹A₁ absorption system in 6-hydroxy-2-formylfulvene (HFF) has been probed under ambient bulk-gas conditions by using polarization-resolved degenerate four-wave mixing (DFWM) spectroscopy. The alleviation of rovibronic congestion and suppression of rotational-branch structure afforded by judicious selection of incident/detected polarizations for the DFWM interaction has enabled refined rotation-tunneling information to be extracted for the lowest-lying singlet excited manifold, ùB₂ (π*π). In contrast to the ultrafast dynamics (τ_pt ≤ 120fs) that characterize the ~X¹A₁ ground electronic state of HFF, the π*←π electron promotion is found to impede intramolecular proton transfer markedly, leading to the near complete quenching of tunneling-induced spectral signatures. The intrinsic dependence of reaction coordinate and proton-transfer efficacy on the nuances of potential-surface topology and transition-state geometry will be discussed in light of these experimental results, with complementary quantum-chemical calculations serving to elucidate the dramatic impact that subtle changes in energy landscape can exert upon unimolecular dynamics.

Laser excitation spectra of the yttrium monoxide (YO) molecule in the ultra violet region between the 280 and 320 nm have been recorded and studied using optical-optical double resonance (OODR) spectroscopy. The YO molecule was prepared by the reaction of laser ablated yttrium atom with oxygen under supersonic jet cooled conditions. Thirteen vibration bands have been observed via the intermediate B²Σ⁺ state from the X²Σ⁺ state. The excited states analyzed so far are generally in good case (c) coupling scheme. Besides the observation of excited Ω = 0.5 and 1.5 sub-states, and ²Σ⁺ state, we have also identified and studied a forbidden transition, the [33.7]⁴Σ⁻ - B²Σ⁺ transition. Molecular constants for the newly observed electronic states were determined by least squares fitting the measured rotational lines. A number of low-lying Λ-S states and Ω sub-states of the YO molecule have been calculated using SA-CASSCF (state-averaged complete active space self-consistent field) followed by MS-CASPT2 (multi-state complete active space second-order perturbation theory). Since the active Y 5p shell is very important to get some low-lying electronic states with the correct principal configurations, the active space consists of 7 electrons in 12 orbitals corresponding to the Y 4d5s5p and O 2p shells. The molecular orbitals from Y 4s4p and O 2s are inactive but are also correlated, whereas the lower core-shells are relaxed only by SA-CASSCF and then kept frozen at the CASPT2 level. Spin-orbit coupling (SOC) is treated via the state-interaction (SI) approach with the one-center atomic mean field integral (AMFI) approximation for one- and two-electron spin-orbit integrals. In the SOC calculations of potential energy curves (PECs), the SA-CASSCF wavefunctions are adopted where the diagonal elements in the SOC matrix are replaced by the corresponding MS-CASPT2 energies calculated above. A comparison of the spectroscopic properties of electronic states determined experimentally and from calculations will be presented.

Studies of the bonding and electronic structure of simple actinide compoundsM. C. Heaven, B. J. Barker and I. O. Antonov, J. Phys. Chem. A, 2014, 118, 10867-10881.T. Steimle, D. L. Kokkin, S. Muscarella and T. Ma, J. Phys. Chem. A, 2015, 119, 9281-9285.C. Linton, A. G. Adam and T. C. Steimle, J. Chem. Phys., 2014, 140, 214305/214301-214305/214307.D. L. Kokkin, T. C. Steimle and D. DeMille, Phys. Rev. A: At., Mol., Opt. Phys., 2014, 90, 062503/062501-062503/062510. are attractive because they provide insight into the chemistry of more complex molecules associated with radioactive waste. These molecules are the most effective venues for developing a synergism between theory and experiment. The primary goal of the present study is to understand and identify different levels of covalency in a series of gas phase actinides and lanthanides containing molecules via the determination of the permanent electric dipole moment, μ, and magnetic g-factors. The electronic spectrum of ThF has been investigated using: a) medium resolution two dimensional (2D)N. J. Reilly, T. W. Schmidt and S. H. Kable, J. Phys. Chem. A, 2006, 110, 12355-12359. ultrahigh field free, Stark, and Zeeman spectroscopy of a supersonically cooled molecular beam sample. A strong band system near 540 nm was detected and the Stark shifts and splitting were analyzed to produce μ values of 1.426(18)D and 0.586(30)D, for the X²∆_3/2 and [18.5] Ω=3/2 states, respectively. Zeeman splittings were analyzed to show that both the ground and excited [18.5] Ω=3/2 states are predominately ²∆_3/2 spin-orbit components. A molecular orbital correlation diagram will be used to rationalize the observed very small μ values, the electronic state distribution, and garner insight into the bonding mechanism.

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M. C. Heaven, B. J. Barker and I. O. Antonov, J. Phys. Chem. A, 2014, 118, 10867-10881.

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C. Linton, A. G. Adam and T. C. Steimle, J. Chem. Phys., 2014, 140, 214305/214301-214305/214307.

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N. J. Reilly, T. W. Schmidt and S. H. Kable, J. Phys. Chem. A, 2006, 110, 12355-12359.;

Knowledge of actinide bonding is essential for nuclear energy and reactor applications, including nuclear waste treatment. Due to its relatively simple electronic structure, thorium oxide (ThO) is an ideal molecule to study actinide bonding. Previous studies have reported visible and near UV band systems that were recorded under high temperature conditions. Spectral congestion significantly complicated the analyses of these data. In the present work we have examined ThO bands under conditions where jet cooling was used to reduce the rotational temperature to approximately 90 K. LIF spectra were recorded over the range 18,000-19,800 cm⁻¹. Several new vibronic bands have been characterized. Some extend the data range for known electronic transitions, while others belong to electronic states that have not been reported previously. Analysis of these data and models for the electronically excited states of ThO will be presented.

r0pt Figure According to the Chapman cycle, during formation, metastable ozone can be stabilized by a third body (M) collision (buffer gas) in the atmosphere. The stabilization occurs through an energy transfer (ET) mechanism from O₃^* to M. The details of this ET are not well known and one of the reasons is the lack of an accurate potential energy surface (PES) including the collision partner. The PES of the O₃-Ar complex is a 6D problem in full-dimensionality, or 3D for rigid O₃. Here we present a global 3D PES for O₃ fixed at equilibrium, interacting with Ar. Highly accurate Davidson-corrected multi-reference configuration interaction (MRCI-f12) energies were computed at 2112 data points. The AUTOSURF code was used to construct the PES automatically, represented by a local interpolating moving least-squares (L-IMLS) method. A global RMS fitting error of 0.6 cm⁻¹ was obtained. Symmetry equivalent minima with a well depth of -229 cm⁻¹ are located above and below the plane of O₃. We present here bound vdW states of the O₃-Ar complex obtained by variational rovibrational calculations, as well as quantum scattering cross-sections for rotationally inelastic collisions.

Metal-ammonia complexes, [M(NH₃)₄]^0,±, are shown theoretically to have a M(NH₃)₄^x+ positively charged core with one, two, or three outer electrons orbiting in its periphery. Our results reveal a new class of molecular entities (solvated electron precursors) which host outer electrons resembling atoms. The observed electronic shell model (1s, 1p, 1d, 2s, 1f, 2p, 2d) differs from that of the hydrogen-like model and resembles the jellium or nuclear shell model. This fact is attributed to the different effective electrostatic potential experienced by the outer electrons. Multi-reference and propagator approaches combined with diffuse basis sets are employed to calculate accurate geometries, ionization energies, electron affinities and vertical excitation energies. Our results are expected to trigger the interest of the experimental spectroscopy community. r5pt Figure

Calculation of rotation-vibration line intensities with sub-percent accuracy has recently become a standard requirement for the applications in retrieval and monitoring of gases in the Earth's atmosphere and potentially in the atmospheres of exoplanets. A major factor in the accurate calculation of intensities is the requirement for a high accuracy ab initio Dipole moment surface (DMS) (e.g. references L.Lodi, J. Tennyson and O.L. Polyansky, Journal of Chemical Physics, 135, 034113, (2011) nd O.L. Polyansky, K. Bielska, M. Ghysels, L. Lodi, N.F.Zobov, J.T.Hodges, J. Tennyson Physical Review Letters, 114, 243001, (2015) . We demonstrate here that the change from the ”good” potential energy surface (PES) to ”excellent” PES, used for the intensity calculations is also important. By ”good” we mean here, for example, the PES a standard deviation of 0.025 cm⁻¹and by ”excellent” - the PES with the standard deviation 0.011 cm⁻¹. Details of studies on H₂OI.I Mizus, A.A. Kyuberis, N.F. Zobov, V.Y. Makhnev, O.L. Polyansky and J. Tennyson Phil. Trans. R. Soc. A, 376, 20170149, (2018) O₃ O.L.Polyansky, N.F. Zobov, I.I Mizus, A.A. Kyuberis. L. Lodi and J. Tennyson JQSRT, 210, 127-135 (2018) HCN and CO₂ molecules will be presented in the talk. L.Lodi, J. Tennyson and O.L. Polyansky, Journal of Chemical Physics, 135, 034113, (2011) a O.L. Polyansky, K. Bielska, M. Ghysels, L. Lodi, N.F.Zobov, J.T.Hodges, J. Tennyson Physical Review Letters, 114, 243001, (2015) ) I.I Mizus, A.A. Kyuberis, N.F. Zobov, V.Y. Makhnev, O.L. Polyansky and J. Tennyson Phil. Trans. R. Soc. A, 376, 20170149, (2018), O.L.Polyansky, N.F. Zobov, I.I Mizus, A.A. Kyuberis. L. Lodi and J. Tennyson JQSRT, 210, 127-135 (2018),

r[0pt]0pt Figure The potential energy surface (PES) of a molecular system constitutes a cornerstone for every theoretical study of spectroscopy and dynamics. We describe here our general code for the automated construction of PESs for van der Waals (vdW) systems composed of two (rigid) fragments. The AUTOSURF suite is designed to completely automate all of the steps and procedures that go into fitting various classes of PESs. The algorithms are based on the local interpolating moving least squares (L-IMLS) methodology, and have many advanced features such as options for data-point placement, and iterative refinement. We have interfaced this fitting approach to popular electronic structure codes such as Molpro and CFOUR to automatically generate ab initio PESs for 3D (atom - general molecule) and 4D (linear molecule - linear molecule) vdWs systems. The niche of these algorithms is to obtain an interpolative representation of high-level ab initio energies with negligible (arbitrarily small) fitting error, enabling a broad community of non-experts in PES fitting methods to bridge electronic structure calculations and spectroscopic and dynamics research. The code is demonstrated here by presenting PESs and analysis of the corresponding rovibrational bound states for 7 highly anisotropic “heavy-light” systems: C₆H⁻-H₂, HC₂NC-H₂, HNC₃-H₂, HC₅N-H₂, C₄H⁻-H₂, MgCCH-H₂, NCCP-H₂.

The Active Thermochemical Tables (ATcT) approach by RuscicB. Ruscic, Active Thermochemical Tables (ATcT) values based on ver. 1.118 of the Thermochemical Network (2015); available at ATcT.anl.govncorporates data for a large number of chemical species from a variety of sources (both experimental and theoretical) and derives a self-consistent network capable of making extremely accurate estimates of quantities such as temperature dependent enthalpies of formation. The network provides rigorous uncertainties, and since the values don’t rely on a single measurement or calculation, the provenance of each quantity is also obtained. To expand and improve the network it is desirable to have a reliable protocol such as the HEAT approachA.Tajti, P. G. Szalay, A. G. Császár, M. Kállay, J. Gauss, E. F. Valeev, B. A. Flowers, J. Vázquez, and J. F. Stanton. JCP 121, (2004):11599.or calculating accurate theoretical data. Anharmonic zero-point-energies are essential for accurate enthalpies of formation even at 0 K. Coupled Cluster based vibrational perturbation theory (VPT2) quickly becomes prohibitively expensive for larger, more chemically relevant molecules. Here we present benchmark work based upon testing the use of B3LYP and MP2 based VPT2 in-place of CCSD(T). The benchmark set includes some species from the original HEAT set^b, as well as some larger organic (C_aH_bO_c) species. We also consider scaled harmonic zero-point-energies based upon recent workM.Kesharwani, B.Brauer and J.M.L. Martin. J.Phys.Chem. A 119,(2015):1701ith the B2PLYP double hybrid functional and comment on its outlook for the same benchmark set as the DFT and MP2 VPT2 approach. The derived methods are implemented in a fully automated computational workflow.

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B. Ruscic, Active Thermochemical Tables (ATcT) values based on ver. 1.118 of the Thermochemical Network (2015); available at ATcT.anl.govi A.Tajti, P. G. Szalay, A. G. Császár, M. Kállay, J. Gauss, E. F. Valeev, B. A. Flowers, J. Vázquez, and J. F. Stanton. JCP 121, (2004):11599.f M.Kesharwani, B.Brauer and J.M.L. Martin. J.Phys.Chem. A 119,(2015):1701w

Photodissociation of carbon monosulfide (CS) in UV-dominated regions, including diffuse interstellar medium and protoplanetary regions, may produce metastable carbon and sulfur in ¹S and ¹D states, which could contribute internal energy to gas-phase chemical reactions. However, unlike its isoelectronic CO molecule, little is known about Vacuum UV (VUV) photodissociation of CS. In the present study, we investigated the C¹Σ⁺−X¹Σ⁺ band of CS. CS is generated by photolysis of CS₂ and then adiabatically expanded into a vacuum chamber. The two-independently-tunable-VUV photodissociation-photoionization spectroscopy coupled with velocity map imaging (VMI) detection was used to measure state-specific photodissociation cross sections and atomic state branching fractions. Our experiment is the first quantitative study of CS in the VUV spectral region.

As a by-product of an ongoing rather comprehensive study of the electronic structure of the lowest valence and Rydberg states of O₂, chiefly singlets and triples, in this contribution we focus on high-spin electronic states, namely, quintets and septets. Although these latter states may be thought of as of pure academic interest, the current calculations show interesting features of their potential energy curves (PECs) which have not been studied and are actually unknown for most diatomics made up of first-row atoms (plus hydrogen and helium). Experimentally, there is essentially no information whatsoever, aside from some indirect evidence of the possible involvement of high-spin species in the spectroscopy or photodissociation processes. Theoretically, there are a few studies, but they are usually issued from early and modest calculations, so the accuracy is not good enough. We report in this contribution an insight into the quintet and septet electronic states of molecular oxygen. Their PECs display a rich and complex structure, and interactions among states which could not be anticipated. We report PECs of valence, Rydberg and ion-pair quintet states as well as of various Rydberg septet states. Most PECs are repulsive, as expected, yet, a few of the high-spin states are bound. Excitation energies are tabulated for all states. Spectroscopic constants are given for the bound states. A case is also presented of a bound sextet state of O₂⁺, along with potential curves of several sextet repulsive states of the cation.