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Updated: Aug 25, 2025

Measurement of Ultrafast Vibrational Coherences in Polyatomic Radical Cations with Strong-Field Adiabatic Ionization
Published on: August 6, 2018
Cryogenic IR and UV spectroscopy of isomer-selected cytosine radical cation
Franco Molina1,2,3,4, Jordan Dezalay1, Satchin Soorkia1
1Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, F-91405 Orsay, France. gilles.gregoire@universite-paris-saclay.fr.
Abstract:
Oxidation of the nucleobases is of great concern for the stability of DNA strands and is considered as a source of mutagenesis and cancer. However, precise spectroscopy data, in particular in their electronic excited states are scarce if not missing. We here report an original way to produce isomer-selected radical cations of DNA bases, exemplified in the case of cytosine, through the photodissociation of cold cytosine-silver (C-Ag+) complex. IR-UV dip spectroscopy of C-Ag+ features fingerprint bands for the two keto-amino cytosine tautomers. UV photodissociation (UVPD) of the isomer-selected C-Ag+ complexes produces the cytosine radical cation (C˙+) without isomerization. IR-UV cryogenic ion spectroscopy of C˙+ allows for the unambiguous structural assignment of the two keto-amino isomers of C˙+. UVPD spectroscopy of the isomer-selected C˙+ species is recorded at a unique spectral resolution. These benchmark spectroscopic data of the electronic excited states of C˙+ are used to assess the quantum chemistry calculations performed at the TD-DFT, CASSCF/CASPT2 and CASSCF/MRCI-F12 levels.
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