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

• Published in: The Journal of chemical physics Vol. 146; no. 22; p. 224309
• Main Authors: Weichman, Marissa L, Cheng, Lan, Kim, Jongjin B, Stanton, John F, Neumark, Daniel M
• Format: Journal Article
• Language: English
• Published: United States 14.06.2017
• ISSN: 1089-7690
• DOI: 10.1063/1.4984963

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 Köppel-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 of CH O up to 2000 cm and of CD O up to 1500 cm above the vibrational origin, using calculated vibronic wave functions. The adiabatic electron affinities of CH O and CD O are determined from the cryo-SEVI spectra to be 1.5689 ± 0.0007 eV and 1.5548 ± 0.0007 eV, respectively, demonstrating improved precision compared to previous work. Experimental peak splittings of <10 cm are resolved between the e and e components of the 6 and 5 vibronic levels. A pair of spin-vibronic levels at 1638 and 1677 cm were predicted in the calculation as the e and e components of 6 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 vibronic levels in the cryo-SEVI spectra also provides direct evidence of vibronic coupling between ground and electronically excited states of methoxy.