Electronic spectra of the protonated indole chromophore in the gas phase

Ivan Alata (1) , Bert Johan (2) , Michel Broquier (1, 3) , Claude Dedonder (1, 3, 2) , Géraldine Féraud (2) , Gilles Grégoire (4) , Soorkia Satchin (3) , Ernesto Marceca (5) , Christophe Jouvet (1, 3, 2)

1 CLUPS - Centre Laser de l'Université Paris Sud
2 PIIM - Physique des interactions ioniques et moléculaires
3 ISMO - Institut des Sciences Moléculaires d'Orsay
4 LPL - Laboratoire de Physique des Lasers
5 INQUIMAE - Instituto de Química Física de los Materiales, Medio Ambiente y Energía [Buenos Aires]

The electronic spectroscopy of cold protonated indole was investigated experimentally and theoretically. Two isomers have been observed in this experiment, the first isomer corresponds to the lowest energy isomer in the calculations, absorbing at ~350 nm and protonated on the C3 atom of the pyrrole ring. According to our calculations, the absorption of the other isomers protonated on carbon atoms (C2, C4, C5, C6 and C7) is in the visible region. Indeed, the absorption of the second isomer observed starts at 488 nm and has been assigned to protonation on the C2 carbon of the pyrrole ring. Since good agreement was obtained between calculated and experimental transitions for the observed isomers, reasonable ab initio transition energies may also be expected for the higher energy isomers protonated on other carbon atoms, which should also absorb in the visible. Protonation on the nitrogen atom leads to a blue-shifted transition with respect to that of the most stable isomer.

Mots clés: protonation sites; excited states; photo-fragmentation spectroscopy; cold ion trap; ab initio calculations; protonation sites.

Domaines: Agrégats Moléculaires et Atomiques [physics.atm-clus]

Ivan Alata, Bert Johan, Michel Broquier, Claude Dedonder, Géraldine Féraud, et al.. Electronic spectra of the protonated indole chromophore in the gas phase. Journal of Physical Chemistry A, 2013, 117 (21), pp.4420-4427. ⟨10.1021/jp402298y⟩. ⟨hal-00724234v2⟩