Threshold behavior in metastable dissociation of multi-photon ionized thymine and uracil

Pandey, R.; Ryszka, M.; da Fonseca Cunha, T.; Lalande, M.; Dampc, M.; Limão-Vieira, P.; Mason, N.J.; Poully, J.C. and Eden, S. (2017). Threshold behavior in metastable dissociation of multi-photon ionized thymine and uracil. Chemical Physics Letters, 684 pp. 233–238.

DOI: https://doi.org/10.1016/j.cplett.2017.06.051

Abstract

Microsecond-timescale HNCO loss has been observed from single-color multi-photon ionized pyrimidine nucleobases in the gas phase. Photon energy thresholds for the metastable channels have been measured at 5.55 ± 0.02 eV for thymine and 5.57 ± 0.02 eV for uracil. We argue that these results can be attributed to accessing the molecules’ S₁ states with additional vibrational energy matching the threshold energy for HNCO loss from the radical cation. Combined with previous photoionization energies, this enables the S₁ adiabatic energies to be deduced: 3.67 ± 0.07 eV for thymine and 3.77 ± 0.07 eV for uracil. These values are consistent with recent calculations.

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