Benzonitrile (C₇H₅N, C_2v, μ_a = 4.5 D) has recently been detected in the interstellar medium (ISM), specifically in the Taurus Molecular Cloud 1 (TMC-1), using both the technique of composite averages¹⁻² and by nine hyperfine-resolved rotational transitions² under 50 GHz. While benzonitrile has been thoroughly studied using infrared and cm-wave spectroscopy, no former studies have examined the rotational spectrum above 160 GHz. Herein, we present the analysis and assignment of the mm-wave rotational spectrum of benzonitrile (vibrational ground state) in the 103 – 350 GHz frequency range, which should assist in future astronomical searches. Additionally, we have completed a two-state least-squares fit of the hitherto unreported, Coriolis-coupled dyad of benzonitrile’s two lowest frequency vibrational modes: ν₂₂ (141 cm⁻¹) and ν₃₃ (163 cm⁻¹), resulting in approximately 3000 transitions per state fit to within experimental accuracy. The two-state fit accounts for many resonances between the two states and 11 nominal interstate transitions. As a result, we have determined the energy gap between the vibrational states (∆E_22,33= 19.108187(7) cm⁻¹) and the Coriolis coupling value (ζ_22,33^a = 0.841(5)). The study demonstrates that the lowest energy fundamentals of benzonitrile follow the previously described pattern of this molecular class. 1. Kalenskii, S. V., Possible Detection of Interstellar Benzonitrile. Proceedings of the Russian-Indian workshop on radio astronomy and star formation, October 10-12, 2016 (eds. I. Zinchenko & P. Zemlyanukha), Institute of Applied Physics RAS, p.43-50, 2017. 2. McGuire, B. A.; Burkhardt, A. M.; Kalenskii, S. V.; Shingledecker, C. N.; Remijan, A. J.; Herbst, E.; McCarthy, M. C. Science 2018, 359 (6372), 202-205.

The Criegee intermediates, which are carbonyl oxides produced in ozonolysis of unsaturated hydrocarbons,R. Criegee and G. Wenner, J. Liebigs Ann. Chem. 564, 9 (1949).lay important roles in the production of OH, aerosols and organic acids in the atmosphere. Criegee intermediates react readily with other atmospheric species such as NO₂, SO₂, (H₂O)₂ and HCl. The reaction of CH₂OO with HCl was reported to be rapid, with a rate coefficient of 4.6×10⁻¹¹ cm³ molecule⁻¹ s⁻¹.Elizabeth S. Foreman, Kara M. Kapnas, Craig Murray, Angew. Chem. Int. Ed. 55, 1 (2016).uantum-chemical calculations indicate that the reaction CH₂OO + HCl proceeds through a barrierless association reaction to form chloromethyl hydroperoxide (CMHP, CH₂ClOOH), which was predicted to have three stable conformations, denoted as gauche-gauche CMHP, anti-CMHP and gauche-anti CMHP; the first two conformers were observed by microwave spectroscopy.C. Cabezas and Y. Endo, ChemPhysChem. 18, 1860 (2017).n this work, a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved infrared (IR) absorption spectra of the reactants and products during the reaction of CH₂OO with HCl in a flow system. CH₂OO was produced from the reaction of O₂ with CH₂I, which was produced via photolysis of CH₂I₂ at 308 nm.Y.-Y. Wang, C.-Y. Chung, and Y.-P. Lee, J. Chem. Phys. 145, 154303 (2016).ime-resolved IR absorption spectra were recorded at resolution 0.25 cm⁻¹. The spectrum of gauche-gauche CMHP was characterized by the absorption bands at 1061.4, 1309.4, 1359.9 cm⁻¹, and the spectrum of gauche-anti CMHP was characterized by the absorption bands at 1054.8, 1310.3, 1359.3 cm⁻¹. The observed wavenumbers, rotational contours and relative intensities agree with those predicted with the B3LYP/aug-cc-PVTZ method; contributions of the hot bands from excited states of the low-lying torsional modes are significant.

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R. Criegee and G. Wenner, J. Liebigs Ann. Chem. 564, 9 (1949).p Elizabeth S. Foreman, Kara M. Kapnas, Craig Murray, Angew. Chem. Int. Ed. 55, 1 (2016).Q C. Cabezas and Y. Endo, ChemPhysChem. 18, 1860 (2017).I Y.-Y. Wang, C.-Y. Chung, and Y.-P. Lee, J. Chem. Phys. 145, 154303 (2016).T

The electrophilic addition of halogens to alkenes is important in organic synthesis. The structure of the reaction intermediate, haloalkyl radical, plays an important role in the stereo specificity of the addition reaction. The simplest intermediate, haloethyl radical C₂H₄X, has two possible geometries: an open (classical) structure and a bridged structure. However, which structure is more stable is controversial because several calculations yield varied results. Experiments using time-resolved X-ray diffractionH. Ihee, M. Lorenc, T. K. Kim, Q. Y. Kong, M. Cammarata, J. H. Lee, S. Bratos, M. Wulff, Science. 2005, 309, 1223.nd UV absorptionA. Kalume, L. George, A. D. Powell, R. Dawes, S. A. Ried, J. Phys. Chem. A. 2014, 118, 6838.ndicated that C₂H₄I has a briedged structure, but our results of Cl + C₂H₄ in solid para-hydrogen (p-H₂) indicated that C₂H₄Cl has an open structure.J. C. Amicangelo, B. Golec, M. Bahou, Y. P. Lee, Phys. Chem. Chem. Phys. 2012, 14, 1014.ven though experiments in noble-gas matrices suggest that C₂H₄Br is open,A. Kalume, L. George, P. Z. El-Khoury, A. N. Tarnovsky, S. A. Reid, J. Phys. Chem. A. 2010, 114, 9919.hereas C₂H₄I is bridged,L. George, A. Kalume, S. A. Reid, Chem. Phys. Lett. 2012, 554, 86.he spectral evidence remains uncertain. We took advantage of the diminished cage effect of p-H₂ to investigate the infrared (IR) spectra of C₂H₄Br and C₂H₄I by irradiating p-H₂ matrices containing C₂H₄ and Br₂ or I₂ with light at varied wavelengths. New spectral lines were grouped according to their behavior upon subsequent annealing and secondary photolysis. The assignments were derived on comparison with scaled vibrational wavenumbers and IR intensities calculated with the B3LYP/aug-cc-pVTZ-pp method. Our preliminary results indicate that lines at 676.9, 776.7, 1068.1, 1148.0, and 3126.8 cm⁻¹are assigned to the 2-bromoethyl radical (C₂H₄Br) in an open form, whereas those at 933.7, 1139.0, 1436.8, and 1609.0 cm⁻¹to the iodoethyl radical (C₂H₄I) in the bridged form. A small amount of C₂H₄Br₂ and C₂H₄I₂ was also observed; their stereochemistry will also be discussed.

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Footnotes:

H. Ihee, M. Lorenc, T. K. Kim, Q. Y. Kong, M. Cammarata, J. H. Lee, S. Bratos, M. Wulff, Science. 2005, 309, 1223.a A. Kalume, L. George, A. D. Powell, R. Dawes, S. A. Ried, J. Phys. Chem. A. 2014, 118, 6838.i J. C. Amicangelo, B. Golec, M. Bahou, Y. P. Lee, Phys. Chem. Chem. Phys. 2012, 14, 1014.E A. Kalume, L. George, P. Z. El-Khoury, A. N. Tarnovsky, S. A. Reid, J. Phys. Chem. A. 2010, 114, 9919.w L. George, A. Kalume, S. A. Reid, Chem. Phys. Lett. 2012, 554, 86.t

When computing vibrational spectra with collocation and localized basis functions such as Gaussian functions, one can choose the distribution of points and of function centers to increase the accuracy or decrease the cpu cost. Here, we compute vibrational energy levels using Gaussian basis functions whose centers are in slabs that include the lower-dimensional hyperplanes on which the Multimode approximation to the potential is based. We use more potential points than basis functions to increase the accuracy, i.e. we use rectangular collocation. The number of Gaussian basis functions is smaller than the number required using the best existing methods. For formaldehyde, the first 50 (100) levels we compute, using 30,000 Gaussians and 120,000 points, in 4D-like slabs, differ from numerically exact levels by 0.3 (0.6) cm-1 (mean absolute error). With 3D-like slabs, the mae for the first 50 (100) levels is 0.17 (0.47) cm-1 with 30,000 basis functions and 0.95 (2.06) cm-1 with 20,000 basis functions. Although we use a multimode-like idea to select Gaussian centers, we use a single point set and there is no need to write the potential in multimode form and no need to neglect high-order terms.

Time-resolved resonance-enhanced Raman spectra of the selenocyanate dimer radical anion, (SeCN)₂^.−, prepared by pulse radiolysis in water, have been obtained and interpreted in conjunction with theoretical calculations to provide detailed information on the molecular geometry and bond properties of the species. The structural properties of the radical are used to develop a molecular perspective on its thermochemistry in aqueous solution. Twelve Stokes Raman bands of the radical observed in the 100-3000cm⁻¹region are assigned in terms of the strongly 140.5cm⁻¹, weakly 550cm⁻¹, and moderately 2095cm⁻¹, enhanced fundamentals, their overtones and combinations. Calculations by range-separated hybrid density functionals (ωB97x and LC-ωPBE) support the spectroscopic assignments of the 140.5cm⁻¹vibration to a predominantly SeSe stretching mode and the features at 550cm⁻¹and 2095cm⁻¹to SeC and CN symmetric stretching modes, respectively. The corresponding bond lengths are 2.957Å, 1.823Å and 1.157Å. A first order anharmonicity of 0.44cm⁻¹determined for the SeSe stretching mode suggests a convergence of vibrational states at an energy  1.4eV, using the Birge–Sponer extrapolation. This value, estimated for the radical confined in solvent cage, compares well with the calculated gas-phase energy, 1.32eV, required for the radical to dissociate into SeCN^. and SeCN⁻ fragments. The enthalpy of dissociation drops to 0.70eV in water when solvent dielectric effects on the radical and its dissociation products upon Se-Se bond scission are incorporated in the calculations. Our findings are compared to analogous symmetric and asymmetric hemibonded radical anions i.e. (SCN)₂^.− and NCSOH^.− to provide insights into relationship between their structure and properties.

Ultrahigh vacuum tip-enhanced Raman spectroscopy (UHV-TERS) is a powerful method combining the rich chemical information of vibrational spectroscopy with the ultrahigh spatial resolution of scanning tunneling microscopy (STM). However, despite of its potential, there is a lack of studies demonstrating the capability of UHV-TERS in investigating chemical reactions and molecular adsorptions under controlled environment. Herein, we use UHV-TERS to investigate adsorption of oxygen (O₂) with cobalt (II) phthalocyanine (CoPc) supported on Ag(111) single crystal surfaces under highly controlled environment, which is the initial step for the oxygen reduction reaction (ORR) using metal Pc catalysts. Two adsorption configurations are primarily observed, assigned as O₂/CoPc/Ag(111) and O/CoPc/Ag(111) based on STM imaging, TERS, isotopologue substitution, and density functional theory (DFT) calculations. Distinct vibrational features are observed for different adsorption configurations such as the ¹⁸O-¹⁸O stretching frequency at 1151 cm⁻¹for O₂/CoPc/Ag(111), and Co-¹⁶O and Co-¹⁸O vibrational frequencies at 661 cm⁻¹and 623 cm⁻¹, respectively, for O/CoPc/Ag(111). DFT calculations show vibrational mode coupling of O-O and Co-O vibrations to the Pc ring, resulting in different symmetries of oxygen-related normal modes for different isotopes. This study establishes UHV-TERS as a chemically sensitive tool for probing catalytic systems at the molecular-scale.