title: Electronic spectra of the protonated indole chromophore in the gas phase.
abstract: The electronic spectroscopy of cold protonated indole was investigated experimentally and theoretically. Two isomers were observed by 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 absorptions of the other isomers protonated on carbon atoms (C2, C4, C5, C6, and C7) are in the visible region. Indeed, the absorption of the second observed isomer starts at 488 nm and was assigned to protonation on the C2 carbon of the pyrrole ring. Because good agreement was obtained between the calculated and experimental transitions for the observed isomers, reasonable ab initio transition energies can also be expected for the higher-energy isomers protonated on other carbon atoms, which should also absorb in the visible region. Protonation on the nitrogen atom leads to a transition that is blue-shifted with respect to that of the most stable isomer.
authors.affiliation: CLUPS (Centre Laser de l'Université Paris-Sud/LUMAT FR 2764), Université Paris-Sud, 91405 Orsay Cedex, France.
authors.forename: Ivan
authors.initials: I
authors.lastname: Alata
authors.forename: Johan
authors.initials: J
authors.lastname: Bert
authors.forename: Michel
authors.initials: M
authors.lastname: Broquier
authors.forename: Claude
authors.initials: C
authors.lastname: Dedonder
authors.forename: Géraldine
authors.initials: G
authors.lastname: Feraud
authors.forename: Gilles
authors.initials: G
authors.lastname: Grégoire
authors.forename: Satchin
authors.initials: S
authors.lastname: Soorkia
authors.forename: Ernesto
authors.initials: E
authors.lastname: Marceca
authors.forename: Christophe
authors.initials: C
authors.lastname: Jouvet
mesh_terms: D005740:Gases / Q000737:chemistry; D007211:Indoles / Q000737:chemistry*; D011522:Protons; D011789:Quantum Theory; D013056:Spectrophotometry, Ultraviolet
chemical_list: D005740:Gases; D007211:Indoles; D011522:Protons