Electronic spectra of linear HC5_5H and cumulene carbene H2_2C5_5

The $1 ^3\Sigma_u^- \leftarrow X^3\Sigma_g^-$ transition of linear HC$_5$H (A) has been observed in a neon matrix and gas phase. The assignment is based on mass-selective experiments, extrapolation of previous results of the longer HC$_{2n+1}$H homologues, and density functional and multi-state CASPT2 theoretical methods. Another band system starting at 303 nm in neon is assigned as the $1 ^1 A_1 \leftarrow X ^1 A_1$ transition of the cumulene carbene pentatetraenylidene H$_2$C$_5$ (B).Comment: 7 pages, 4 figures, 5 table

High resolution electronic spectroscopy of a non-linear carbon chain radical C6H4+.

The electronic spectrum of a member of a so-far-unstudied class of carbon chain radicals was observed:a nonlinear and noncyclic species. The spectrum was observed more or less accidentally around 604 nm when scanning for coincidences with diffuse interstellar band features in a hydrocarbon plasma. The observed spectrum has a clear rotational and K-type structure. Simulation of the spectrum allowed an accurate determination of the molecular constants of the carrier

Electronic Transition of Ferrocenium: Neon Matrix and CASPT2 Studies

Electronic absorptions of ferrocenium starting at 632.5 nm were measured in a 6 K neon matrix following mass-selective deposition of the ions. The spectrum shows clear vibrational structure and provides the best-yet resolved view of the electronic states of this cation. The absorption system is identified as the 1 2E1′ ← X 2E2′ transition (D5h symmmetry) on the basis of vertical excitation energies and oscillator strengths calculated at the CASPT2 level. Vibrational bands in the spectrum are assigned with the aid of the ground-state frequencies calculated with the DFT method

Structure and electronic transitions of C7H4O2+ and C7H5O2+ ions: neon matrix and theoretical studies

C7H4O2+ and C7H5O2+ ions and the respective neutrals have been investigated by absorption spectroscopy in neon matrixes following mass selection of ions produced from salicylic acid. Three electronic transitions starting at 649.6, 431.0, and 372.0 nm are detected for C7H4O2+ and assigned on the basis of CASPT2 energies and Franck–Condon simulations as the excitations from the X 2A″ to the 1 2A″, 2 2A″, and 3 2A″ electronic states of 6-(oxomethylene)-2,4-cyclohexadien-1-one ion (A+). Absorptions commencing at 366.4 nm are observed for C7H5O2+ and assigned to the 1 2A′ ← X 2A′ electronic transition of (2-hydroxyphenyl)methanone ion (J+). Neutralization of J+ leads to the appearance of four absorption systems attributed to the 4 2A″, 3 2A″, 2 2A″, and 1 2A″ ← X 2A″ transitions of J with origin bands 291.3, 361.2, 393.8, and 461.2 nm

Electronic Spectra of Corannulenic Cations and Neutrals in Neon Matrices and Protonated Corannulene in the Gas Phase at 15 K

Three absorption systems starting at 624.1, 601.2, and 590.0 nm were detected in a 6 K neon matrix following deposition of mass selected m/z = 250 ions produced from corannulene vapour in a hot cathode ion source. The two latter systems were also observed after deposition of neutral corannulene in solid neon with concomitant bombardment of the matrix with argon ions. The features in the absorption spectrum are assigned to the 42A′′  ←  X2A′′ transition of cylobutadieno-benzo[ghi]fluoranthene cation and to the 32A′  ←  X2A′′ and 32A′′  ←  X2A′ transitions of two Jahn-Teller structures of bowl-shaped corannulene cations, respectively. The assignment is based on excitation energies calculated with the SAC-CI and CASPT2 methods. The electronic absorption spectrum of protonated corannulene has onsets at 515.1 and 398.8 nm in a neon matrix, following deposition of a mass-selected beam produced by reactions of corannulene with EtOH2+. The absorptions are assigned, on the basis of theoretical predictions, to the 3,41A  ←  X1A transitions. The electronic spectrum was also recorded in the gas phase using a resonant multiphoton fragmentation technique in an ion trap at vibrational and rotational temperatures of 15 K. The 3,41A  ←  X1A transitions are observed with origin bands at 521 ± 1 nm and 396.4 ± 0.1 nm. The 31A excited electronic state indicates fast internal conversion of ≈ 5 fs, while the 41A state has a lifetime of ≈ 0.2 ps. A distinct vibrational pattern is discernible in the 41A  ←  X1A transition

Electronic spectra of oxygen containing polycyclic hydrocarbon cations and the protonated analogues

The electronic transitions of 9-fluorenone FL+ and 2,3,6,7-dibenzotropone DBT+ cations were detected in 6 K neon matrices following a mass-selective deposition. The absorptions at 649.2 and 472.2 nm are assigned to the 2 2B1←X̃2A2 FL+ and 22A′←X̃2A′ DBT+ transitions. Absorption spectra of protonated 9-fluorenone H+-FL and 2,3,6,7-dibenzotropone H+-DBT have also been measured. Protonation of the oxygenated polycyclic aromatic hydrocarbons is carried out in a hot cathode source via in situ produced protonated ethanol. Vibrationally resolved absorptions commencing at 423.3 nm of H-FL+ and two band systems of H-DBT+ with origins at 502.4 and 371.5 nm are assigned to the 21A′←X̃1A′ electronic transition of 9-hydroxy-fluorenyl cation and 1 1A←X̃1A, 2 1A←X̃1A of 2,3,6,7-dibenzocycloheptenol cation. The assignments are based on vertical excitation energy calculations with time dependent density functional theory, symmetry adapted cluster configuration interaction, and MS-CASPT2 methods

Higher energy electronic transitions of HC2n+1H+ (n=2–7) and HC2n+1H (n=4–7) in neon matrices

Electronic absorption spectra of linear HC2n+1H+ (n=2–7) were recorded in 6 K neon matrices following their mass-selective deposition. Four new electronic band systems are identified; the strongest ˜E Π2g/u←˜X Π2u/g lies in the UV and the second most intense ˜C Π2g/u←˜X Π2u/g is located in the visible range. The known ˜A Π2g/u←˜X Π2u/g absorption is an order of magnitude weaker than ˜C Π2g/u←˜X Π2u/g. Transitions to the ˜B and ˜D states are also discussed. The wavelengths of the HC2n+1H+ (n=2–7) electronic systems obey a linear relation as a function of the size of the cations, similar to other carbon chains. The ˜B Σu−3←˜X Σg−3 transition in the UV of neutral HC2n+1H (n=4–7) has also been identified upon photobleaching of the cations trapped in the matrices

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

Two electronic transitions at 512.3 and 250 nm of linear-C5H+ are detected following mass-selective deposition of m/z = 61 cations into a 6 K neon matrix and assigned to the 1 1Π←X 1Σ+ and 1 1Σ+←X 1Σ+ systems. Five absorption systems of l-C5H 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 2Π to 1 2Δ, 1 2Σ −, 1 2Σ+, 2 2Π, and 3 2Π 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

Electronic absorption spectra of protonated anthracenes and phenanthrenes, and their neutrals in neon matrices

Electronic spectra of three isomers of protonated anthracene and five isomers of protonated phenanthrene have been detected in 6 K neon matrices following deposition of mass-selected m/z = 179 cations produced from dihydro-anthracene or -phenanthrene. The cations exhibit moderately intense band systems in the 400-550 nm range. Corresponding neutrals have been observed in the UV. The absorptions are assigned to specific isomers of the protonated species on the basis of time-dependent density functional theory calculations. The astrophysical relevance of protonated anthracenes and phenanthrenes as candidates for carriers of diffuse interstellar bands is discussed