Probing the vibrational spectroscopy of the deprotonated thymine radical by photodetachment and state-selective autodetachment photoelectron spectroscopy via dipole-bound states† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c5sc00704f

Deprotonated thymine can exist in two different forms, depending on which of its two N sites is deprotonated: N1[T–H] or N3[T–H] . Here we report a photodetachment study of the N1[T–H] isomer cooled in a cryogenic ion trap and the observation of an excited dipole-bound state. Eighteen vibrational levels of the dipole-bound state are observed, and its vibrational ground state is found to be 238 5 cm 1 below the detachment threshold of N1[T–H] . The electron affinity of the deprotonated thymine radical (N1[T–H]c) is measured accurately to be 26 322 5 cm 1 (3.2635 0.0006 eV). By tuning the detachment laser to the sixteen vibrational levels of the dipole-bound state that are above the detachment threshold, highly non-Franck–Condon resonant-enhanced photoelectron spectra are obtained due to stateand mode-selective vibrational autodetachment. Much richer vibrational information is obtained for the deprotonated thymine radical from the photodetachment and resonantenhanced photoelectron spectroscopy. Eleven fundamental vibrational frequencies in the low-frequency regime are obtained for the N1[T–H]c radical, including the two lowest-frequency internal rotational modes of the methyl group at 70 8 cm 1 and 92 5 cm .