Diradical carbenes have long been recognized as important intermediates in a range of chemical processes, with the carbene's chemical reactivity being sensitive to the particular ground-state electronic structure. We have undertaken an investigation of chlorocarbene (HCCl) by seeding CHCl₃ into a Ne/He/H₂ mixture and passing this mixture through a pulsed slit discharge. In the discharge environment, the CHCl₃ undergoes a double Cl atom removal process through a combination of electron dissociative attachment and hydrogen abstraction. The subsequent jet expansion cools the HCCl diradical to a 32 K rotational temperature. With the goal of assisting the search for HCCl chemistry in interstellar molecular clouds, the rotational constants for the ground singlet state of both the ³⁵Cl and ³⁷Cl isotopologues are determined through least-squares fits of ground-state combination differences to an asymmetric top Watson Hamiltonian. A Watson Hamiltonian is also used to extract rotational constants for the nominally (100) vibrationally excited state, with a highly mixed combination band (nominally (012), one quantum of H-C-Cl bend plus two quanta of C-Cl stretch) of comparable intensity found within a few wavenumbers (cm⁻¹) of the CH stretch band origin. The proximity of these two bands and the comparable infrared intensities of both combination and fundamental bands points towards a highly mixed state with strong anharmonic coupling between these two zeroth order modes. We quantify the anharmonic coupling in a 2x2 matrix deperturbation treatment and find it to be similar in magnitude to the previously measured spin-orbit coupling constants between the singlet and nearby lying triplet manifold of states.

We have generated NO₃ in a supersonic free jet expansion, and observed laser induced fluorescence ( LIF ) and two-color resonant four-wave mixing ( 2C-R4WM ) signals. We have measured dispersed fluorescence ( DF ) spectra from single vibronic levels. Among the vibrational levels observed in the DF spectrum from the vibration-less level, the ν₁ and ν₃ fundamental regions (  ∼ 1050 and  ∼ 1500 cm⁻¹ regions, respectively ) are now active for discussion, and thus we have tried to measure the rotationally resolved 2C-R4WM spectraM. Fukushima and T. Ishiwata, 71st ISMS, paper RF01 (2016). The 2C-R4WM spectrum of the ν₃ fundamental region is consistent with a previous infra-red investigationK. Kawaguchi, et al., J. Mol. Spectrosco. 268, 85 (2011). and that of ν₁ leads to the identification of the K = 0 and N = 1 level of the ν₁ fundamental for the first time. We have found an additional level near ν₁M. Fukushima and T. Ishiwata, 68th ISMS, paper WJ03 (2013). and the 2C-R4WM spectrum of the level shows two rotational transitions separated by 0.27 cm⁻¹. Although the 0.27 cm⁻¹ separation is about 10 times larger than the spin splitting,  ∼ 0.025 cm⁻¹, of the K = 0 and N = 1 levels at the other a₁’ levels with l = 0, such as vibration-less and ν₁ ( the latter value of which, 0.025 cm⁻¹, cannot be resolved under our instrumental resolution ), the two transitions are thought to correspond to those terminating to spin sub-levels, J = 0.5 and = 1.5, at the present. We have assigned the additional level to 3ν₄ (a₁′) with l = ±3. For Σ vibronic levels with K = 0, such as v_d = 1 and l = 1, of a ²Π electronic state, it is well known that ²Σ⁽⁺⁾ and ²Σ⁽⁻⁾ vibronic levels have relatively large Ω- or ρ-type doubling due to non-zero Λ, in spite of the Σ vibronic levelsJ. Hougen, J. Chem. Phys. 36, 519 (1964) It is thought that the unexpectedly large spin splitting, 0.27 cm⁻¹, is induced by spin-vibration interaction, which has been discussed for degenerate vibronic levels of non-degenerate electronic states, ²Σ and ³Σ, of linear polyatomic moleculesA. J. Merer and J. M. Allegretti, Can. J. Phys. 49, 2859 (1971).

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Footnotes:

M. Fukushima and T. Ishiwata, 71st ISMS, paper RF01 (2016).. K. Kawaguchi, et al., J. Mol. Spectrosco. 268, 85 (2011)., M. Fukushima and T. Ishiwata, 68th ISMS, paper WJ03 (2013)., J. Hougen, J. Chem. Phys. 36, 519 (1964). A. J. Merer and J. M. Allegretti, Can. J. Phys. 49, 2859 (1971)..

Whereas benzyl radical, a prototype of aromatic free radicals, had attracted much attention from spectroscopists for the subject of large molecular radicals, chloro-substituted benzyl–type radicals have been little studied, presumably due to the difficulties associated with production in corona discharge from precursors. The weak C-Cl bond can be easily dissociated in high voltage corona discharge, S. Y. Chae, M. Lim, and S. K. Lee, Chem. Phys. Lett. 664, 242-245 (2016).eading to the cleavage of benzene ring. During past years, we have concentrated on the spectroscopic observation of chloro-substituted methylbenzyl radicals in a technique of corona excited supersonic expansion using a pinhole-type glass nozzle which has been well developed in this lab. From the experiments, we could succeed the observation of vibronic emission spectra of chloro-substituted methylbenzyl radicals from 3- and 4-chloro-o-xylenes. From the analysis of the spectra observed, we can identify the radical species produced in corona discharge and determine the electronic energies of the D₁ → D₀ transition. The variation of the electronic transition energies with the positions and types of substituents have been clearly explained by means of the additivity rule Y. W. Yoon, S. Y. Chae, and S. K. Lee, Chem. Phys. Lett. 644, 167-170 (2016).nd shape of the unoccupied lowest molecular orbitals (LUMO) which corresponds to the upper state of the electronic transition. In this presentation, the observation scheme of the chloro-substituted benzyl-type radicals and analysis of the spectra for the identification of the radical species generated will be discussed, together with the introduction of the method for the explanation of substituent effect C.  Branciard-Larcher, E. Migirdicyan, and J. Baudet Chem. Phys. 2, 95-106 (1973).n the electronic transition energy of the benzyl-type radicals.

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Footnotes:

S. Y. Chae, M. Lim, and S. K. Lee, Chem. Phys. Lett. 664, 242-245 (2016).l Y. W. Yoon, S. Y. Chae, and S. K. Lee, Chem. Phys. Lett. 644, 167-170 (2016).a C.  Branciard-Larcher, E. Migirdicyan, and J. Baudet Chem. Phys. 2, 95-106 (1973).o

The Criegee intermediates (CI) play critical roles in atmospheric chemistry. CH₂OO is the simplest CI and its characterization is important for investigations of reaction mechanisms and molecular structure. In this work, high-resolution spectra of the OO-stretching (ν₆) mode of CH₂OO in the range of 880\textendash932 cm⁻¹have been recorded using a quantum cascade laser (QCL) system coupled with a multi-pass Herriott cell. The CH₂OO was produced from the reaction of CH₂I + O₂ in a flowing mixture of CH₂I₂/O₂ (1/213) at 3.2 Torr upon irradiation at 248 nm with an excimer laser. The spectrum was recorded by step-scanning the QCL with a step size of  0.0016 cm⁻¹; its wavelength was calibrated with a C₂H₄ reference cell and a germanium etalon. Over one thousand lines were assigned and used for fitting of molecular constants of CH₂OO. Furthermore, the rotational perturbations on the high-J levels of K_a = 3, K_a = 6, and K_a ≥ 11 were observed.

The ground electronic state of potassium monoxide (KO) has yet to be conclusively assigned, despite both experimental and theoretical investigations of this species. The ground state is either ²Π_i (as for LiO and NaO) or ²Σ⁺ (as for RbO and CsO), both of which are predicted to lie close in energy for KO. To solve this problem, we have conducted millimeter-wave direct absorption spectroscopy of KO. This species was synthesized via the reaction of potassium vapor, generated by a Broida-type oven, with nitrous oxide. We have found patterns that we have identified as the Ω = 3/2 and 1/2 ladders of a ²Π_i state, as well as a ²Σ⁺ state. Rotational and fine structure constants have been accurately determined assuming the ²Π_i and ²Σ⁺ assignments.

The stannylidene (SnCH₂) molecule has been detected for the first time in the gas phase by supersonic expansion/laser spectroscopy. This transient molecule was produced in an electric discharge through a dilute mixture of tetramethyltin [(CH3)₄Sn] in high-pressure argon and studied by laser induced and dispersed fluorescence through the ~B ¹B₂ - ~X ¹A₁ transition. The vibronic energy levels of the ground and excited states have been measured for both SnCH₂ and SnCD₂. The observed vibrational frequencies, partially resolved rotational band contours, deuterium isotope shifts, and electronic excitation energies are in accord with our predictions from ab initio calculations. This novel species has an unusual tin-carbon double bond in the ground state. It is the third in the series of X=CH₂ (X = Si, Ge and Sn) group IVA vinylidene species we have been able to produce and study in the gas phase.

The SiCF radical was produced in an electric discharge through a dilute mixture of trimethyl(trifluoromethyl)slilane (CH₃)₃SiCF₃ in high-pressure argon. Using our high-resolution pulse amplified ring dye laser system, the laser induced fluorescence of the 0-0 band of the òΣ⁺- ~X²Π_i transition has been rotationally resolved (linewidths   0.015 cm⁻¹) for the first time. The subsequent rotational analysis paired with previous ab initio calculations^a allowed the determination of the ground and excited state SiC bond lengths. We find a Si-C double bond in the ground state and an unusual Si-C triple bond in the excited state. Finally, further low-resolution spectra were obtained to determine better values for the excited state vibrational frequencies. ^aC. J. Evans and D. J. Clouthier, J. Chem. Phys., 117, 6439-6445 (2002)

Ce atom reactions with alkyamines are carried out in a pulsed-laser ablation molecular beam source and characterized by mass-analyzed threshold ionization (MATI) spectroscopy. The MATI spectra of CeNR (R = CH₃, C₂H₅, and C₃H₇) formed by Ce reactions with H₂NR exhibit two band systems, separated by 78, 74, and 72 cm⁻¹, respectively. In contrast, the MATI spectrum of CeNC₂H₅ formed in the Ce + HN(CH₃)₂ reaction show two band systems with a much larger separation, 130 cm⁻¹. These separations are attributed to the spin-orbit (SO) splitting from the Ce 4f¹ electron. The different splittings between CeNR from the reactions of primary amines and CeNC₂H₅ from the reaction of secondary amine are due to their different structures. The CeNR complexes from the primary amines have acyclic structures with Ce double bonding to the N atom, whereas CeNC₂H₅ from the dimethylamine has a cyclic structure with Ce bonding to the N atom and one of the C atoms. The considerably smaller SO splittings in the CeNR species suggests that N coordination has a stronger quenching effect on the SO coupling of the Ce 4f electron than the C coordination.

Anion photoelectron imaging spectra of two butenoxyl (3-buten-1-oxyl and 3-buten-2-oxyl) radical isomers are presented. The neutral electron affinities are comparable to those measured for saturated alkoxy radicals [Ramond et al., J. Chem. Phys. 112, 1158 (2000)], and the measured term energies for the à ²A state of both isomers is approximately 0.1 eV. However, spectra of the two isomers exhibit distinct differences, particularly in the low electron binding energy signal that may be due to the presence of structural isomers. The experimental spectra are analyzed with supporting MP2 calculations and Franck-Condon simulations. Overall, the results underscore how the electronic properties vary with subtle changes in alkoxy radical structure, which may have implications for atmospheric photochemistry, as alkoxy radicals are key intermediates of the tropospheric oxidation of volatile organic compounds.

Saturated and unsaturated alcohols are released into the atmosphere by vegetation and industrial activities and become radicals in the environment. These radical species are highly reactive toward other atmospheric species and are key intermediates of the oxidation of volatile organic compounds in the troposphere. In this talk we will investigate anion photoelectron imaging (PEI) of the 2-propenol radical at photon energies of 2.33 eV and 3.49 eV as an example of these radical species. DFT (B3LYP) and ab initio (MP2) calculations will be used to further elaborate on the transitions of these species and compare theory to experimental results.

Iodomethyl radical (CH₂I) is relevant to atmospheric chemistry, especially marine boundary layer dynamics, with recent attention arising from its use as novel precursor for Criegee intermediates (CH₂OO). As a first step towards the spectroscopic investigation of a Criegee intermediate, we have pursued high resolution characterization of the CH₂I radical in our slit jet discharge spectrometer. The methyl iodide radical is generated by seeding CH₂I₂ into a Ne/He/H₂ mixture in a pulsed slit discharge, produced through either electron dissociative attachment to form iodine anions or hydrogen abstraction of iodine, with subsequent cooling in a supersonic expansion to 16 K. Infrared absorption in the CH symmetric stretch vibrational band is observed at high single-to-noise ratio (S/N = 25:1), yielding a symmetric stretch band origin at 3046.9527 ±0.0006  cm⁻¹. The sub-Doppler rotational structure is fitted to a rigid-rotor Hamiltonian with spin-rotation coupling, generating principal rotational constants and the spin-orbit coupling tensor for the vibrationally excited state. Interestingly, an extensive search for the asymmetric stretch mode yielded null results, despite simple bond-dipole model predictions of three-fold larger absorption intensities for the asymmetric vs. symmetric stretch band. We conclude that the asymmetric stretch absorption intensity must be at least a factor of 25 below that of the symmetric stretch. Ab initio calculations indicate that enhancement of the symmetric vs. asymmetric stretch intensity arises from "charge sloshing" motion of electrons in the highly polar carbon-iodine bond of the correct A₁ symmetry.