Electronic absorptions of the benzylium cation

C1 - Journal Articles RefereedThe electronic transitions of the benzylium cation (Bz(+)) are investigated over the 250-550 nm range by monitoring the photodissociation of mass-selected C(7)H(7)(+)-Ar(n) (n = 1, 2) complexes in a tandem mass spectrometer. The Bz(+)-Ar spectrum displays two distinct band systems, the S(1)←S(0) band system extending from 370 to 530 nm with an origin at 19,067 ± 15 cm(-1), and a much stronger S(3)←S(0) band system extending from 270 to 320 nm with an origin at 32,035 ± 15 cm(-1). Whereas the S(1)←S(0) absorption exhibits well resolved vibrational progressions, the S(3)←S(0) absorption is broad and relatively structureless. Vibronic structure of the S(1)←S(0) system, which is interpreted with the aid of time-dependent density functional theory and Franck-Condon simulations, reflects the activity of four totally symmetric ring deformation modes (ν(5), ν(6), ν(9), ν(13)). We find no evidence for the ultraviolet absorption of the tropylium cation, which according to the neon matrix spectrum should occur over the 260 - 275 nm range [A. Nagy, J. Fulara, I. Garkusha, and J. Maier, Angew. Chem., Int. Ed. 50, 3022 (2011)]

Electronic Spectra of Gas-Phase Polycyclic Aromatic Nitrogen Heterocycle Cations: Isoquinoline(+) and Quinoline(+)

C1 - Journal Articles RefereedElectronic spectra of the gas-phase isoquinoline(+)-Ar and quinoline(+)-Ar complexes are recorded using photodissociation spectroscopy by monitoring the Ar loss channel. The D(3)←D(0) and D(4)←D(0) band origins for isoquinoline(+)-Ar are observed at 15245 ± 15 cm(-1) and 21960 ± 15 cm(-1), respectively, whereas for quinoline(+)-Ar they appear at 16050 ± 15 cm(-1) and 21955 ± 15 cm(-1), respectively. Strong vibronic progressions for the D(3)←D(0) band systems of both isoquinoline(+)-Ar and quinoline(+)-Ar are modeled and assigned in terms of ring deformation and carbon-carbon stretch vibrational modes using time-dependent density functional theory calculations in conjunction with Franck-Condon simulations. The properties of the isoquinoline(+) and quinoline(+) molecules are compared with those of the isoelectronic naphthalene(+) molecule. The existence of strong progressions in the visible spectra of isoquinoline(+)-Ar and quinoline(+)-Ar suggests that the corresponding isoquinoline(+) and quinoline(+) molecular cations are unlikely to be responsible for diffuse interstellar bands

Electronic spectrum of 9-methylanthracenium radical cation

The predissociation spectrum of the cold, argon-tagged, 9-methylanthracenium radical cation is reported from 8000 cm-1 to 44 500 cm-1. The reported spectrum contains bands corresponding to at least eight electronic transitions ranging from the near infrared to the ultraviolet. These electronic transitions are assigned through comparison with ab initio energies and intensities. The infrared D1←D0 transitions exhibit significant vibronic activity, which is assigned through comparison with TD-B3LYP excited state frequencies and intensities, as well as modelled vibronic interactions. Dissociation of 9-methylanthracenium is also observed at high visible-photon energies, resulting in the loss of either CH2 or CH3. The relevance of these spectra, and the spectra of other polycyclic aromatic hydrocarbon radical cations, to the largely unassigned diffuse interstellar bands, is discussed

Electronic spectrum of the propargyl cation (H2C3H+) tagged with Ne and N-2

The Ã(1)A1 ← X̃(1)A1 band system of the propargyl cation (H2C3H(+)) is measured over the 230-270 nm range by photodissociation of mass-selected H2C3H(+)-Ne and H2C3H(+)-N2 complexes in a tandem mass spectrometer. The band origin occurs at 37 618 cm(-1) for H2C3H(+)-Ne and 37 703 cm(-1) for H2C3H(+)-N2. Ground and excited state ab initio calculations for H2C3H(+) using the MCSCF and coupled-cluster (CC) response methods show that the ion has C2v symmetry in the ground X̃(1)A1 and excited Ã(1)A1 states and that the strong vibronic progression with a spacing of 630 cm(-1) is due to the C-C stretch vibrational mode, ν 5