l0pt Figure The Renner-Teller effect describes the coupling of a symmetry-reducing molecular vibration with a two-fold degenerate electronic state. Its discovery goes back to work of Herzberg and Teller, who realized in 1933 that the potential energy surface of a triatomic, linear molecule splits into two as soon as the molecule is bent. In this work, we show that a very similar, yet unknown type of non-adiabatic coupling can even occur for diatomic (!) molecules.
This seems absurd at first sight, but becomes possible as soon as the diatomic molecule ist embedded in a spherically symmetric confinement. In this case, its translational degrees of freedom become quantized and can couple to electronically degenerate states in a very similar fashion as predicted by Renner-Teller effect theory. To our knowledge, it is the first time that this novel type of non-adiabatic coupling has been investigated either in theory or experiment.[1]
We demonstrate this effect for the experimentally accessible case of NO embedding in a C₆₀. Endofullerenes, in particular those carrying a radical molecule, are highly topical objects of ongoing research in molecular spectroscopy, reaction chemistry and carbon-based nanomaterial design. Also, suitable confinements in molecular traps for quantum information and quantum computing will produce a similar effect of nonadiabatic coupling as predicted by our study.
[1] A.W. Hauser and J.V. Pototschnig, J .Phys. Chem. A, 2022, DOI:10.1021/acs.jpca.1c10970

Photoelectron spectroscopy is a powerful technique to investigate the electronic structure and chemical bonding of anions and the corresponding neutrals upon electron detachment. Here, we use our electrospray ionization photoelectron spectroscopy apparatus, which couples a cryogenically-cooled 3D Paul trap and a high resolution imaging system to get the vibrational and electronic information about three azolide: pyrazolide, pyrrolide and imidazolide. Besides the expected conventional dipole bound state, a core-excited dipole bound state is observed in pyrazolide with the neutral core in its first excited electronic state. And a completely different threshold behavior is observed for pyrrolide and imidazolide with a similar pi type HOMO: a d-wave-dominated spectrum is found for pyrrolide and an s-wave-dominated spectrum is found for imidazolide.

We report an evaluation of the importance of London dispersion in moderately large (up to 32 heavy atoms) organic molecules by means of a molecular torsion balanceTsybizova‡, A.; Fritshe‡, L.; Gorbachev‡, V.; Miloglyadova, L.; Chen, P. J. Chem. Phys. 2019, 151, 234304hose conformations “weigh” London forces against cation-π(aryl) in the absence of solvent. The experimental gas-phase study is performed using cryogenic ion vibrational predissociation (CIVP) spectroscopy covering both the N-H and the effectively "deperturbed" N-DGorbachev, V.; Miloglyadova, L.; Tsybizova, A.; Chen, P. Rev. Sci. Instrum. 2021, 92, 083002tretching modes, taking into account possible perturbation due to the tag molecule.Tsybizova, A.; Paenurk, E.; Gorbachev, V.; Chen, P. J. Phys. Chem. A 2020, 124, 41, 8519, 234304he gas-phase data is supported by solid-state FT-IR spectroscopy, single-crystal x-ray crystallography, and is accompanied by DFT calculations, including an extensive search and analysis of the accessible conformations. We begin with the unsubstituted molecular torsion balance, and then step up the complexity systematically by adding alkyl groups incrementally as dispersion energy donors (DEDs) to achieve a degree of chemical complexity comparable to what is typically found in transition states for many regio- and stereoselective reaction in organic and organometallic chemistry. We find clear evidence for the small attractive contribution by DEDs, as had been reported in other studies, but we also find that small individual contributions by London dispersion, when they operate in opposition to other weak non-covalent interactions, produce composite effects on the structure that are difficult to predict intuitively, or by modern quantum chemical calculations. The experimentally observed structures, together with a reasonable value for a reference cation-π interaction, indicate that the pairwise interaction between two tert-butyl groups, in the best case, is modest. Moreover, the visualization of the conformational space, and comparison to spectroscopic indicators of structure, as one steps up the complexity of the manifold of non-covalent interactions, makes clear that in silico predictive ability for the structure of moderately large, flexible, organic molecules falters sooner than one might have expected.Gorbachev, V.; Tsybizova, A.; Miloglyadova, L.; Chen, P. J. Am. Chem. Soc. 2022, submittedhtml:<hr /><h3>Footnotes: Tsybizova‡ , A.; Fritshe‡ , L.; Gorbachev‡ , V.; Miloglyadova, L.; Chen, P. J. Chem. Phys. 2019, 151, 234304w Gorbachev, V.; Miloglyadova, L.; Tsybizova, A.; Chen, P. Rev. Sci. Instrum. 2021, 92, 083002s Tsybizova, A.; Paenurk, E.; Gorbachev, V.; Chen, P. J. Phys. Chem. A 2020, 124, 41, 8519, 234304T Gorbachev, V.; Tsybizova, A.; Miloglyadova, L.; Chen, P. J. Am. Chem. Soc. 2022, submitted

l0pt Figure The optical spectra of the diatomic PdS radical in the gas phase have been investigated for the first time through a combination of laser-induced fluorescence (LIF) and single vibronic level emission spectroscopy. The [22.3] ³Σ⁻ − X ³Σ⁻ transition system containing sixteen vibrational bands was identified in the LIF spectra in the energy range of 22,030 − 23,400 cm⁻¹. Rotationally resolved spectra and analysis enabled a determination of the molecular structures in the upper and lower states, involving the rotational constants, the vibrational constants, the spin-orbit splittings, and the vibrational isotope shifts. The emission transitions from the [22.3] state down to the ground state and to the low-lying A ³Π state were recorded, by which the spin-orbit splittings of A ³Π_2,1,0^−,+ were determined. A comparison of the bond lengths (and the vibrational frequencies) of the VIII group monosulfide radicals (NiS/PdS/PtS) reveals the relativistic effects in the Pd and Pt atoms.

Equation-of-Motion Coupled cluster (EOM-CC) is a preferred method for high-precision electronic spectroscopy due to its size-extensivity and implicit inclusion of higher-order excitation effects in the electronic wavefunction. The accuracy of the EOM-CC wave function can be controlled by truncating the cluster operator, T, and/or excitation operator, R, at increasing levels of excitation. Within core-hole calculations (XPS, XAS/NEXAFS, XES, and RIXS), the inclusion of triple excitations, in concert with the core-valence separation (CVS), is critical in order to accurately treat orbital relaxation effects; however, including triple excitations unavoidably leads to high computational cost. Instead, we propose two alternative approaches: first, in Transition-Potential Coupled Cluster (TP-CCSD), orbital relaxation is explicitly included in the reference orbitals through the use of a fractional-occupation SCF calculation followed by CVS-EOM-CCSD. Second, the CVS-STEOMEE-CCSD+cT method extends the similarity-transformed EOM-CC approach of Nooijen with triple excitations, but only for the inexpensive core ionization potentials. We benchmark both methods for first-row K-edge vertical ionization and excitation energies of 14 small molecules, compared to the accurate but extremely expensive CVS-EOMEE-CCSDT method, as well as select comparisons to experimental gas-phase XAS. We find that both methods are effective in treating the orbital relaxation of core-hole states, with absolute energy errors below 0.5 eV and relative errors for peak positions typically below 0.3 eV. Both methods are also computationally efficient: TP-CCSD has the same computational cost as the less-accurate CVS-EOM-CCSD method, while CVS-STEOMEE-CCSD+cT is only marginally more expensive for a small number of excitations. For large numbers of excitated states, the STEOM-based approach may be significantly faster.

Polycyclic aromatic hydrocarbons (PAH) have been surmised as carriers of the diffuse interstellar bands (DIB), hundreds of unidentified spectral lines in the infrared through ultraviolet regions. These PAH are often thought to be in their cationic or neutral forms in the interstellar medium, although there have been models that feature these molecules as the primary carriers of negative charge in dense interstellar clouds, rather than just free electrons. We monitored the photodetachment cross section as a function of wavelength for tetracene radical anion (C₁₈H₁₂⁻) to explore the resonances of the tetracene radical anion above the detachment threshold. The observed electronic states closely align with a previously reported absorption spectrum of the molecule, with one major exception. Sharp features (less than 10 cm⁻¹) corresponding to a long-lived Feschbach resonance of the molecule were found in the near-IR. This corresponds to a lifetime of no faster than  600 fs, a much longer lifetime than typically observed for above detachment resonances. These features can potentially be used to detect the presence of anionic polyaromatic species in the interstellar medium. However, we were not able to make any assignments based on our spectra for tetracene and available DIB data. Still, by acquiring photoelectron spectra at these anion excited electronic states, we identify specific photodetachment channels by which these resonances relax to the ground neutral electronic state. These features will be compared to the anthracene radical anion (C₁₄H₁₀⁻) and the tetracenyl anion to explore the effect of PAH size and dehydrogenation on these resonances. In addition, we will report on possible fragmentation in the UV spectral region mediated by these resonances. Finally, photoelectron spectra are collected using slow electron velocity-map imaging (SEVI), yielding high precision electron affinity values and T₁ term energies for tetracene, as well as identifying active vibrations in these transitions. Interestingly, the T₁ state in the tetracene radical anion photoelectron spectrum features highly non-Franck Condon activity, most likely due to vibronic coupling. The anion resonances shown here along with the photoelectron spectra acquired have interesting implications for the possibility of tetracene as a negative charge carrier in the interstellar medium.

Fluorescence-detected photothermal mid-infrared (F-PTIR) spectroscopy is demonstrated and used to characterize chemical composition within phase-separated domains of pharmaceutical materials. Infrared and Raman spectroscopic imaging are powerful techniques for generating detailed chemical images based on a sample’s spectrum. Previous study on optically detected photothermal infrared (O-PTIR) improved the spatial resolution by probing the temperature-induced refractive index change but are potentially prone to the high background in scattering media. Fluorescence-detected photothermal mid-infrared (F-PTIR) spectroscopy (Fig. 1) is proposed, providing dual-level chemical discrimination based on both fluorescence and infrared absorption. F-PTIR relies on the intrinsic sensitivity of the fluorescence quantum efficiency to temperature. Therefore, fluorescence can serve as a sensitive probe (SNR over 100) for reporting on highly localized and selective infrared absorption. The theoretical spatial resolution of F-PTIR is ultimately limited by fluorescence microscopy and the thermal diffusivity of the sample instead of the infrared wavelength. Following proof-of-concept measurements with model systems of silica gel and polyethylene glycol particles, F-PTIR measurements were used to probe chemical composition within phase-separated domains of ritonavir within copovidone polymer matrices of relevance in the production of pharmaceutical final dosage forms.

A direct deperturbation analysis for the experimental rovibronic term values belonging to the first three electronic states of the CN radical has been performed using an iterative solution of the inverse spectroscopic problem based on a rigorous coupled-channel approximation. Besides potential energy curves (PECs), the non-adiabatic energy matrix explicitly included the spin-orbit and Coriolis coupling functions between the X²Σ⁺, A²Π and B²Σ⁺ states. The regular perturbation caused by the remote doublet states was taken into account by the introduction of so-called Λ-doubling parameters as an implicit function of the interatomic distance. The initial set of the deperturbed PECs was defined in analytical extended Morse oscillator (EMO) form while the non-adiabatic coupling functions were given as the properly morphed ab initio electronic matrix elements V. A. Terashkevich, E.A. Pazyuk, and A.V. Stolyarov. Journal of Quantitative Spectroscopy and Radiative Transfer, 276, 107916, 2021 The resulting PECs and non-adiabatic parameters reproduce the overall set of experimental energy levels with an accuracy of about 0.01-0.02 cm⁻¹, which is almost comparable with their uncertainty of measurement.The work was supported by the Russian Science Foundation (RSF) (grant No.22-23-00272)

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Footnotes:

V. A. Terashkevich, E.A. Pazyuk, and A.V. Stolyarov. Journal of Quantitative Spectroscopy and Radiative Transfer, 276, 107916, 2021. The work was supported by the Russian Science Foundation (RSF) (grant No.22-23-00272).

l0pt Figure Water vapor absorption in the near-ultraviolet region is essential to describing the energy budget of Earth, but little spectroscopic information is currently available since it is a challenging spectral region for both experimental and theoretical studies. A continuous-wave cavity ring-down spectroscopic experiment was built to record the weak absorption of water vapor in the near-UV region around 415 nm. This is a region that is still missing in laboratory measurements. A minimum absorption coefficient detection of around 4×10⁻¹⁰ cm⁻¹ was reached and over 40 ro-vibrational transitions of H₂¹⁶O determined in this work. A comparison of line positions and intensities determined in this work to the most recent HITRAN2020 database will be presented. We calculate water vapor absorption cross-sections from our measurements and compare them with recent observations (Pei et al., 2019Pei, et al., Journal of Geophysical Research: Atmospheres; 124(24):14310-14324. Du et al., 2013Du et al., Geophysical Research Letters; 40(17):4788-4792. Dupré et al., 2005Dupré et al., The Journal of Chemical Physics; 123(15): 154307 Wilson et al., 2016Wilson et al., Journal of Quantitative Spectroscopy and Radiative Transfer; 295(170): 194-199. Lampel et al., 2017Lampel et al., Atmospheric Chemistry and Physics; 17(2): 1271–1295. and simulations (Gordon et al., 2022Gordon et al., Journal of Quantitative Spectroscopy and Radiative Transfer; 277..

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Footnotes:

Pei, et al., Journal of Geophysical Research: Atmospheres; 124(24):14310-14324.; Du et al., Geophysical Research Letters; 40(17):4788-4792.; Dupré et al., The Journal of Chemical Physics; 123(15): 154307; Wilson et al., Journal of Quantitative Spectroscopy and Radiative Transfer; 295(170): 194-199.; Lampel et al., Atmospheric Chemistry and Physics; 17(2): 1271–1295.) Gordon et al., Journal of Quantitative Spectroscopy and Radiative Transfer; 277.)

The applications of the shock wave research are multi modal. The potential of the shock wave is a large amount of energy is transferred to the material within a very short timescale, leading to the formation of new chemical species and the kinetics of product formation can be studied. Far from the laboratory, shock waves play an important role in controlling the physical and chemical evolution of the interstellar medium (ISM). In the ISM, shock waves are generated due to supernovae explosions, bipolar outflows and stellar winds. However, the application of shock waves to study the chemistry of the ISM is a relatively new area of research. One of the objectives of our research is to identify new possible shock tracers in the low velocity shocked regions of the ISM. Shock induced decomposition of C₆₀ (one of the interstellar building blocks of dusts) was explored in situ with the help of a UV-Vis spectrometer and a monochromator. The integrated emission spectrum reveals the presence of C₂ features with a broad continuum and was affected by self-absorption. The broad continuum is likely due to the combined effect of the black-body emission from small carbon particles and the recurrent fluorescence of various carbon clusters produced via the dissociation of C₆₀. The emission spectrum of C₂ was computed using Exocross module and the column density of the C₂ units were determined.