Substituent effects on vibrational and electronic excitation spectra of pyridone tautomers and ions: The case of the cyano group

International audienceIn this theoretical work, we computed the equilibrium geometries and a set of rotational and vibrational spectroscopic parameters for cyano substituted 2-pyridones neutral or cationic and their tautomers (cyano 2-hydroxypyridines). We examined also the effect of tautomerism equilibrium on those systems. In our analysis, we mostly focused on the perturbations induced by the CN group on the electronic structure and on the spectroscopy of 2-pyridone/2-hydroxypyridine block. Moreover, we investigated the pattern of their low lying electronic states at both the PBE0/aug-cc-pVDZ Density Functional Theory (DFT) and the CASSCF/aug-cc-pVTZ levels of theory. Vertical excitation spectra and both adiabatic and vertical ionization energies were performed

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.)