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Laser-induced fluorescence and dispersed-fluorescence spectroscopy of the ?2E?X?2A1 transition of jet-cooled calcium methoxide (CaOCH <sub/>3</sub> ) radicals
摘要： Laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the ?A2E ? ?X2A1 electronic transition of the calcium methoxide (CaOCH3) radical have been obtained under jet-cooled conditions. Complete active space self-consistent field and coupled-cluster calculations on the free radical were performed to aid the assignment of vibronic transitions observed in the LIF/DF spectra. In addition to dominant spectral features that are well reproduced by vibrational frequencies and Franck-Condon (FC) factors calculated ab initio, the FC matrix for the ?A2E ? ?X2A1 electronic transition contains considerable off-diagonal elements that connect (i) the CaO-stretch (ν4) mode and non-CaO stretch modes and (ii) the asymmetric CaOC stretch (ν3) and the CaOC bending (ν8) modes. The Jahn-Teller and pseudo-Jahn-Teller interactions involving the ?2E state as well as the spin-orbit interaction induce additional vibronic transitions that are not allowed under the Born-Oppenheimer approximation. Additionally, anharmonic vibrational terms in the ground state induce transitions that are forbidden in the harmonic-oscillator approximation. Spin-orbit splitting has been observed for several vibrational levels of the ?2E state, and an essentially constant value was measured at all levels accessed in the LIF experiment. Implications of the present spectroscopic investigation to the proposed schemes of laser-cooling MOCH3 (M = alkaline earth metals) molecules and detection of time-reversal-symmetry-violating interactions are discussed.
关键词： calcium methoxide,laser cooling,spin-orbit interaction,Jahn-Teller effect,Franck-Condon factors,vibronic transitions,CaOCH3,Laser-induced fluorescence,pseudo-Jahn-Teller effect,dispersed-fluorescence spectroscopy
更新于2025-09-19 17:13:59
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Revealing Long-Range Substituent Effects in the Laser-Induced Fluorescence and Dispersed Fluorescence Spectra of Jet-Cooled CH <sub/><i>x</i> </sub> F <sub/> 3– <i>x</i> </sub> CH <sub/>2</sub> O ( <i>x</i> = 1, 2, 3) Radicals
摘要： The B?←X? laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of the atmospherically important β-monofluoro ethoxy (MFEO), β,β-difluoro ethoxy (DFEO), and β,β,β-trifluoro ethoxy (TFEO) radicals were recorded with vibronic resolution under jet-cooled conditions. To simulate the spectra, Franck-Condon factors were obtained from quantum chemical computations carried out at the CAM-B3LYP/6-311++G(d,p) level of theory. The simulations reproduce well both the LIF and DF spectra. Both conformers (G and T) of MFEO and one (G) of the two conformers of DFEO contribute to the LIF spectrum. A comparison between the experimental and calculated spectra confirms the expected long-range field effects of the CHxF3?x group on electronic transition energies and bond strengths, especially in the excited electronic (B?) state. Although TFEO has only one conformer, its LIF spectrum is highly congested, which is attributed to the interaction between CO stretch and the ?CF3 internal rotation.
关键词： Laser-Induced Fluorescence,Molecular Structure,Spectroscopy,Quantum Chemistry,Fluoroethoxy Radicals,Jet-cooled,Dispersed Fluorescence
更新于2025-09-12 10:27:22
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Laser-Induced Fluorescence and Dispersed Fluorescence Spectroscopy of Jet-Cooled Isopentoxy Radicals
摘要： The B?-X? laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of jet-cooled isopentoxy radicals have been obtained. The LIF spectrum of isopentoxy lacks strong transitions to the CO-stretch levels that are typical for alkoxy radicals. Instead, it contains two low-frequency vibrational progressions due to large-amplitude motions of the GG’ and GG conformers involving torsion of the C1C2C3H dihedral angle. Other vibronic bands observed in the LIF spectrum are attributed to the TG conformer. Molecular carriers of the vibronic transitions in the LIF spectrum are identified by comparing the experimentally obtained spectrum and the simulated one. DF spectra of the GG and TG conformers are dominated by strong vibrational progressions of the CO-stretch mode when the origin or the CO-stretch band is pumped. When non-CO-stretch bands are pumped, the DF spectra are dominated by combination bands of the CO-stretch and the pumped mode. ?-X? separations of the GG, and TG conformers were also determined from the DF spectra.
关键词： Isopentoxy Radicals,Conformers,Laser-Induced Fluorescence,Vibrational Progressions,Jet-Cooled,Dispersed Fluorescence Spectroscopy
更新于2025-09-11 14:15:04