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The Adiabatic Ionization Energy and Triplet T1 Energy of Jet-Cooled Keto-Amino Cytosine.

Authors :
Lobsiger S
Leutwyler S
Source :
The journal of physical chemistry letters [J Phys Chem Lett] 2012 Dec 06; Vol. 3 (23), pp. 3576-80. Date of Electronic Publication: 2012 Nov 26.
Publication Year :
2012

Abstract

Gas-phase cytosine exists in five different tautomer/rotamer forms 1, 2a, 2b, 3a, and 3b. We determine the threshold ionization energy (IE) of the keto-amino tautomer 1 as 8.73 ± 0.02 eV, using resonant two-photon ionization mass spectrometry in a supersonic molecular beam via the (1)ππ* excited state. This is the first IE threshold measurement for the biologically relevant tautomer 1. The IE of the thermal gas-phase mixture of cytosine has been measured as 8.60 ± 0.05 eV by Kostko et al. using single-photon VUV photoionization [Phys. Chem. Chem. Phys., 2010, 12, 2860]. Given the tautomer distribution and ionization energies calculated in that work, our determination of the keto-amino tautomer IE implies that the IE measured by Kostko et al. is dominated by the enol-amino tautomers 2a and 2b. Upon excitation of keto-amino cytosine to its (1)ππ* state, relaxation occurs to a lower-lying long-lived state. The IE threshold measured via this state places its energy about 0.69 eV below the (1)ππ* state, in good agreement with the triplet T1 energy of keto-amino cytosine calculated by several high-level ab initio methods. The identification of keto-amino cytosine T1 is the basis for characterizing the intersystem crossing rates into and the photochemical reactions of this long-lived state.

Details

Language :
English
ISSN :
1948-7185
Volume :
3
Issue :
23
Database :
MEDLINE
Journal :
The journal of physical chemistry letters
Publication Type :
Academic Journal
Accession number :
26290991
Full Text :
https://doi.org/10.1021/jz301719h