Photoionization Spectroscopy of Nucleobasesand Analogues in the Gas Phase UsingSynchrotron Radiation as Excitation LightSource

International audienceWe review here the photoionization and photoelectron spectroscopy ofthe gas phase nucleic acid bases adenine, thymine, uracil, cytosine, and guanine, aswell as the three base analogues 2-hydroxyisoquinoline, 2-pyridone, andδ-valerolactam in the vacuum ultraviolet (VUV) spectral regime. The chapterfocuses on experimental work performed with VUV synchrotron radiation andrelated ab initio quantum chemical calculations of higher excited states beyondthe ionization energy. After a general part, where experimental and theoreticaltechniques are described in detail, key results are presented by order of growingcomplexity in the spectra of the molecules. Here we concentrate on (1) the accuratedetermination of ionization energies of isolated gas phase NABs and investigationof the vibrational structure of involved ionic states, including their mutual vibroniccouplings, (2) the treatment of tautomerism after photoionization, in competitionwith other intramolecular processes, (3) the study of fragmentation of these molecularsystems at low and high internal energies, and (4) the study of the evolution ofthe covalent character of hydrogen bonding upon substitution, i.e., examination ofelectronic effects (acceptor, donor, etc.)