Low-lying vibronic level structure of the ground state of the methoxy radical: Slow electron velocity-map imaging (SEVI) spectra and Koppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations

摘要

A joint experimental and theoretical study is reported on the low-lying vibronic level structure of the ground state of the methoxy radical using slow photoelectron velocity-map imaging spectroscopy of cryogenically cooled, mass-selected anions (cryo-SEVI) and Koppel-Domcke-Cederbaum (KDC) vibronic Hamiltonian calculations. The KDC vibronic model Hamiltonian in the present study was parametrized using high-level quantum chemistry, allowing the assignment of the cryo-SEVI spectra for vibronic levels ofCH(3)O up to 2000cm(-1) and ofCD(3)O up to 1500cm(-1) above the vibrational origin, using calculated vibronic wave functions. The adiabatic electron affinities of CH3O and CD3O are determined from the cryo-SEVI spectra to be 1.5689 +/- 0.0007eVand 1.5548 +/- 0.0007eV, respectively, demonstrating improved precision compared to previous work. Experimental peak splittings of < 10 cm(-1) are resolved between the e(1/2) and e(3/2) components of the 61 and 51 vibronic levels. A pair of spin-vibronic levels at 1638 and 1677 cm(-1) were predicted in the calculation as the e(1/2) and e(3/2) components of 62 levels and experimentally resolved for the first time. The strong variation of the spin-orbit splittings with a vibrational quantum number is in excellent agreement between theory and experiment. The observation of signals from nominally forbidden a(1) vibronic levels in the cryo-SEVI spectra also provides direct evidence of vibronic coupling between ground and electronically excited states of methoxy. Published by AIP Publishing.