Electronic transitions of C5H+ and C5H: neon matrix and CASPT2 studies

Abstract

Two electronic transitions at 512.3 and 250 nm of linear-C 5 H + are detected following massselective deposition of m/z = 61 cations into a 6 K neon matrix and assigned to the 1 1 Π ← X 1 Σ + and 1 1 Σ + ← X 1 Σ + systems. Five absorption systems of l-C 5 H with origin bands at 528,7, 482.6, 429.0, 368.5, and 326.8 nm are observed after neutralization of the cations in the matrix and identified as transitions from the X 2 Π to 1 2 ∆, 1 2 Σ − , 1 2 Σ + , 2 2 Π, and 3 2 Π electronic states. The assignment to specific structures is based on calculated excitation energies, vibrational frequencies in the electronic states, along with simulated Franck-Condon profiles. Published by AIP Publishing. [http://dx

Disentangling Electronic Spectra of Linear and Cyclic Hydrogenated Carbon Cluster Cations, C2n+1H+ (n = 3–10)

“…The spectra are all similar in appearance, each displaying sharp peaks arranged in two prominent vibronic progressions, suggesting that the clusters share a common structural motif. Wavelengths for the origin transitions depend linearly on the number of constituent carbon atoms (Figure ), establishing a trend, which, when extrapolated, fits with the origin transition of linear C 5 H + (250.1 nm), whose spectrum has been measured in a neon matrix . There is a strong correlation between the calculated adiabatic transition energies for the linear C 2 n +1 H + ( n = 3–8) clusters and the measured origin transition energies, albeit with a constant energy offset (see Figure S8 in the Supporting Information).…”

“…There is a strong correlation between the calculated adiabatic transition energies for the linear C 2 n +1 H + ( n = 3–8) clusters and the measured origin transition energies, albeit with a constant energy offset (see Figure S8 in the Supporting Information). On the basis of the excited-state calculations and the previous C 5 H + matrix investigation, the observed band systems are assigned to 1 1 Σ + ← X̃ 1 Σ + electronic transitions, which are predicted to have very large oscillator strengths ( f = 2.6 for C 7 H + , f = 3.3 for C 9 H + , f = 3.9 for C 11 H + , f = 4.5 for C 13 H + , f = 4.9 for C 15 H + , and f = 5.2 for C 17 H + based on ωB97X-D/cc-pVDZ TD-DFT-level calculations). The large oscillator strengths are consistent with our observation that it was easy to saturate the transitions such that it was necessary to severely attenuate the tunable OPO beam to avoid power broadening the bands.…”

“…Wavelengths for the origin transitions depend linearly on the number of constituent carbon atoms (Figure 5), establishing a trend, which, when extrapolated, fits with the origin transition of linear C 5 H + (250.1 nm), whose spectrum has been measured in a neon matrix. 7 There is a strong correlation between the calculated adiabatic transition energies for the linear C 2n+1 H + (n = 3−8) clusters and the measured origin transition energies, albeit with a constant energy offset (see Figure S8 in the Supporting Information). On the basis of the excited-state calculations and the previous C 5 H + matrix investigation, 7 the observed band systems are assigned to 1 1 Σ + ← X ̃1Σ + electronic transitions, which are predicted to have very large oscillator strengths (f = 2.6 for C 7 H + , f = 3.3 for C 9 H + , f = 3.9 for C 11 H + , f = 4.5 for C 13 H + , f = 4.9 for C 15 H + , and f = 5.2 for C 17 H + based on ωB97X-D/cc-pVDZ TD-DFT-level calculations).…”

“…In this paper, we present and discuss electronic spectra of protonated carbon clusters containing between 7 and 21 carbon atoms. Although an electronic spectrum has been measured for C 5 H + trapped in a neon matrix, to our knowledge, there are no previously reported electronic spectra for larger C 2 n +1 H + clusters. The C 2 n +1 H + clusters discussed in this paper span a size range over which they are expected to go from possessing linear structures to adopting cyclic structures such that for certain sizes linear and cyclic isomers coexist .…”

Electronic Absorption Spectra of H2C6O+ Isomers: Produced by Ion–Molecule Reactions

“…On the basis of the calculated vertical excitation energies and the oscillator strengths (Table ) as well as the ground state stabilities (Chart ) of B + and D + , one cannot firmly deduce the carrier for the 497 and 354 nm absorptions. However, the structure of B + produced via dissociative ionization of TBrC is analogous to that of the C 6 H 4 + isomer: three-carbon-member ring with aliphatic chain ( T + ) generated from 1,2-dibromobenzene under similar discharge conditions . MS-CASPT2 calculation predicts a strong electronic transition ( f = 0.2) at 4.45 eV (280 nm) for neutral D which was not observed (see Supporting Information, Table SI1).…”