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1. Quantum state control on the chemical reactivity of a transition metal vanadium cation in carbon dioxide activation

   https://doi.org/10.1039/C9CP00575G  

   Chang, Yih Chung; Xu, Yuntao; Ng, Cheuk-Yiu (March 2019, Physical Chemistry Chemical Physics)

   By combining a newly developed two-color laser pulsed field ionization-photoion (PFI-PI) source and a double-quadrupole–double-octopole (DQDO) mass spectrometer, we investigated the integral cross sections ( σ s) of the vanadium cation (V + ) toward the activation of CO 2 in the center-of-mass kinetic energy ( E cm ) range from 0.1 to 10.0 eV. Here, V + was prepared in single spin–orbit levels of its lowest electronic states, a 5 D J ( J = 0–4), a 5 F J ( J = 1–5), and a 3 F J ( J = 2–4), with well-defined kinetic energies. For both product channels VO + + CO and VCO + + O identified, V + (a 3 F 2,3 ) is found to be greatly more reactive than V + (a 5 D 0,2 ) and V + (a 5 F 1,2 ), suggesting that the V + + CO 2 reaction system mainly proceeds via a “weak quintet-to-triplet spin-crossing” mechanism favoring the conservation of total electron spins. In addition, no J -state dependence was observed. The distinctive structures of the quantum electronic state selected integral cross sections observed as a function of E cm and the electronic state of the V + ion indicate that the difference in the chemical reactivity of the title reaction originated from the quantum-state instead of energy effects. Furthermore, this work suggests that the selection of the quantum electronic states a 3 F J ( J = 2–4) of the transition metal V + ion can greatly enhance the efficiency of CO 2 activation. 

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2. Quantum electronic control on chemical activation of methane by collision with spin–orbit state selected vanadium cation

   https://doi.org/10.1039/D0CP04333H  

   Ng, Cheuk-Yiu; Xu, Yuntao; Chang, Yih-Chung; Wannenmacher, Anna; Parziale, Matthew; Armentrout, P. B. (January 2021, Physical Chemistry Chemical Physics)

   null (Ed.)

   By coupling a newly developed quantum-electronic-state-selected supersonically cooled vanadium cation (V + ) beam source with a double quadrupole-double octopole (DQDO) ion–molecule reaction apparatus, we have investigated detailed absolute integral cross sections ( σ 's) for the reactions, V + [a 5 D J ( J = 0, 2), a 5 F J ( J = 1, 2), and a 3 F J ( J = 2, 3)] + CH 4 , covering the center-of-mass collision energy range of E cm = 0.1–10.0 eV. Three product channels, VH + + CH 3 , VCH 2 + + H 2 , and VCH 3 + + H, are unambiguously identified based on E cm -threshold measurements. No J -dependences for the σ curves ( σ versus E cm plots) of individual electronic states are discernible, which may indicate that the spin–orbit coupling is weak and has little effect on chemical reactivity. For all three product channels, the maximum σ values for the triplet a 3 F J state [ σ (a 3 F J )] are found to be more than ten times larger than those for the quintet σ (a 5 D J ) and σ (a 5 F J ) states, showing that a reaction mechanism favoring the conservation of total electron spin. Without performing a detailed theoretical study, we have tentatively interpreted that a weak quintet-to-triplet spin crossing is operative for the activation reaction. The σ (a 5 D 0 , a 5 F 1 , and a 3 F 2) measurements for the VH + , VCH 2 + , and VCH 3 + product ion channels along with accounting of the kinetic energy distribution due to the thermal broadening effect for CH 4 have allowed the determination of the 0 K bond dissociation energies: D 0 (V + –H) = 2.02 (0.05) eV, D 0 (V + –CH 2 ) = 3.40 (0.07) eV, and D 0 (V + –CH 3 ) = 2.07 (0.09) eV. Detailed branching ratios of product ion channels for the titled reaction have also been reported. Excellent simulations of the σ curves obtained previously for V + generated by surface ionization at 1800–2200 K can be achieved by the linear combination of the σ (a 5 D J , a 5 F J , and a 3 F J ) curves weighted by the corresponding Boltzmann populations of the electronic states. In addition to serving as a strong validation of the thermal equilibrium assumption for the populations of the V + electronic states in the hot filament ionization source, the agreement between these results also confirmed that the V + (a 5 D J , a 5 F J , and a 3 F J ) states prepared in this experiment are in single spin–orbit states with 100% purity. 

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3. Probing the Electronic Manifold of MgCl with Millimeter-Wave Spectroscopy and Theory: (3) ² Σ ⁺ and (4) ² Σ ⁺ States

   https://doi.org/10.1021/acs.jpca.4c05458  

   Herman, T J; Ravi, R; Schuurman, M S; DeYonker, N J; Field, R W; Ziurys, L M (November 2024, The Journal of Physical Chemistry A)

   The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been observed in two new electronic excited states, (3)2Σ+ and (4)2Σ+, using direct absorption methods. The molecule was synthesized in a mixture of Cl2, argon and magnesium vapor. For the (3)2Σ+ state, multiple rotational transitions were measured in the v = 0 level for all six isotopologues (24Mg35Cl, 24Mg37Cl, 25Mg35Cl, 25Mg37Cl, 26Mg35Cl, 26Mg37Cl), as well as up to v = 13 for 24Mg35Cl. For the (4)2Σ+ state, less intense spectra were recorded for 24Mg35Cl (v = 0-2). Equilibrium rotational parameters were determined for both states for 24Mg35Cl, as well as rotational constants and 25Mg hyperfine parameters for the other isotopologues. A perturbation was observed between rotational levels of the two states due to an avoided crossing. Computations were also carried out at the CASPT2 and MRCISD+Q levels, and the resulting bond lengths for (3)2Σ+ and (4)2Σ+ states agree well with the experimental values of re = 2.536 Å and 2.361 Å. The computations show that the (3)2Σ+ state has a double-well potential; however, the state behaves as a single well with unperturbed vibrational levels up to v = 13 due to non-adiabatic coupling with the (4)2Σ+ state. 

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4. Sub-Doppler infrared spectroscopy of resonance-stabilized hydrocarbon intermediates: ν ₃ / ν ₄ CH stretch modes and CH ₂ internal rotor dynamics of benzyl radical

   https://doi.org/10.1039/c7cp05776h  

   Kortyna, A.; Samin, A. J.; Miller, T. A.; Nesbitt, D. J. (January 2017, Physical Chemistry Chemical Physics)

   Highly reactive benzyl radicals are generated by electron dissociative attachment to benzyl chloride doped into a neon–hydrogen–helium discharge and immediately cooled to T rot = 15 K in a high density, supersonic slit expansion environment. The sub-Doppler spectra are fit to an asymmetric-top rotational Hamiltonian, thereby yielding spectroscopic constants for the ground ( v = 0) and first excited ( v = 1, ν 3 , ν 4 ) vibrational levels of the ground electronic state. The rotational constants obtained for the ground state are in good agreement with previous laser induced fluorescence measurements (LIF), with vibrational band origins ( ν 3 = 3073.2350 ± 0.0006 cm −1 , ν 4 = 3067.0576 ± 0.0006 cm −1 ) in agreement with anharmonically corrected density functional theory calculations. To assist in detection of benzyl radical in the interstellar medium, we have also significantly improved the precision of the ground state rotational constants through combined analysis of the ground state IR and LIF combination differences. Of dynamical interest, there is no evidence in the sub-Doppler spectra for tunneling splittings due to internal rotation of the CH 2 methylene subunit, which implies a significant rotational barrier consistent with partial double bond character in the CC bond. This is further confirmed with high level ab initio calculations at the CCSD(T)-f12b/ccpVdZ-f12 level, which predict a zero-point energy corrected barrier to internal rotation of Δ E tun ≈ 11.45 kcal mol −1 or 4005 cm −1 . In summary, the high-resolution infrared spectra are in excellent agreement with simple physical organic chemistry pictures of a strongly resonance-stabilized benzyl radical with a nearly rigid planar structure due to electron delocalization around the aromatic ring. 

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5. Assigning quantum labels and improving accuracy for the ro-vibrational eigenstates of H3+ calculated using ScalIT

   https://doi.org/10.3389/fphy.2022.996001  

   Sarka, János; Poirier, Bill (October 2022, Frontiers in Physics)

   In a recent article [AIP Adv. 11, 045033 (2021)], we carried out exact quantum dynamical calculations and computed ro-vibrational energy levels and wave functions for the H 3 + molecular ion up to the dissociation threshold (at J = 46) using a recently developed potential energy surface (PES) [Mol. Phys. 117, 1663 (2019)]—arguably, the most accurate to date —together with the ScalIT suite of parallel codes. In this work, we further improved the convergence accuracy and range of our ScalIT calculations for all J values up to J = 20 to a few 10 –5  cm −1 (or better). In addition, we performed an ab initio assignment of the ro-vibrational energy levels, providing vibrational ‘ v 1 , v 2 , | l |’ and rotational ‘ J , G , U , K ’ quantum labels for more than 2,200 ro-vibrational states, including every single 0 ≤ J ≤ 20 state up to and above the barrier to linearity at 10,000 cm −1 . The main underlying motivation of our work is to provide a list of reliably labeled, spectroscopically accurate energy levels in a format that can be used in spectroscopic line lists, which are based on both experimental and theoretical levels. Such line lists are of huge importance in various astrochemical and astrophysical contexts. 

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