Electronic spectrum of the propargyl cation (H2C3H+) tagged with Ne and N2

Abstract

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.

Electronic spectrum and photodissociation chemistry of the linear methyl propargyl cation H2C4H3+

“…24 Calculated vibrational frequencies of the complexes are provided in the Supplemental Material (Table S2) (Figure 2e), which was recently measured using the same technique. 23 Notably, there is only a slight shift of the H 2 C 4 H 3 + origin to higher energy with respect to the H 2 C 3 H + origin, and the main progression has the same spacing (630 cm −1 ) in the two spectra. 23 These observations imply that H 2 C 4 H 3 + and H 2 C 3 H + are structurally similar with an acetylenic hydrogen atom replaced by a methyl group.…”

“…23 Notably, there is only a slight shift of the H 2 C 4 H 3 + origin to higher energy with respect to the H 2 C 3 H + origin, and the main progression has the same spacing (630 cm −1 ) in the two spectra. 23 These observations imply that H 2 C 4 H 3 + and H 2 C 3 H + are structurally similar with an acetylenic hydrogen atom replaced by a methyl group. For H 2 C 3 H + the dominant progression was assigned to the C-C stretch vibrational mode, ν 5 , with Franck-Condon activity associated with a lengthening of the C-C bond in the excited state.…”

“…indene + -Ar, 18 indole + -Ar, 22 H 2 C 3 H + -N 2 and H 2 C 3 H + -Ne. 23 All calculations were performed with the Gaussian 09 program suite. 24 Calculated vibrational frequencies of the complexes are provided in the Supplemental Material (Table S2) (Figure 2e), which was recently measured using the same technique.…”

“…For H 2 C 3 H + the dominant progression was assigned to the C-C stretch vibrational mode, ν 5 , with Franck-Condon activity associated with a lengthening of the C-C bond in the excited state. 23 Although the methyl group has little effect on the main C-C stretch progression, it does give rise to other progressions that contribute to spectral congestion. Figure 3, there is a reasonably good match between experimental and simulated spectra, although the calculations predict a somewhat shorter 11 n 0 progression than observed experimentally, suggesting that the C-C bond elongation in the excited state exceeds the calculated value (0.10Å).…”

Direct IR Absorption Spectra of Propargyl Cation Isolated in Solid Argon

“… 18 should be the combination band (ν 3 + ν 5 ) of H 2 C 3 H + -Ar. In addition, the A 1 A 1 ← X 1 A 1 electronic transition of H 2 CCCH + in the neon matrix, and that tagged with Ne and N 2 were measured in the spectral region of 230–270 nm 22 . In contrast, the electronic transitions of c-C 3 H 3 + are expected to appear at less than 200 nm, but no experimental values for the same have been reported in any conditions 20 .…”