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

Electronic Spectrum of Dihydrogenated Buckminsterfullerene in a 6 K Neon Matrix

Vibrationally resolved electronic absorption spectrum of 1,2-dihydrogenated[60]fullerene has been recorded in a 6 K neon matrix after mass-selected deposition of m/z = 722 cations produced from reaction of protonated methane and C60 in an ion source. One system has the origin band at 688.5 ± 0.1 nm and another commencing at 404.8 ± 0.1 nm. Theoretical computations were used to calculate the relative energies of three isomers of dihydrogenated[60]fullerene and time-dependent density functional theory predicted the vertical excitations to 50 electronic states

Structure of C6HF+ and C6F2+ fragment ions from fluorobenzenes : electronic spectra in 6 K neon matrices

The fragment ions C6HF+ and C6F2+ produced from fluorobenzenes in a discharge source were trapped in 6 K neon matrices after mass selection. A strong absorption system is detected in the visible range starting at 586.3 nm for C6HF+ and 569.3 nm for C6F2+. Vibrationally resolved fluorescence commencing at the same wavelengths is observed upon laser excitation into each absorption band of these cations. The absorptions are assigned to the A2Πg ← X2Πu and A2Π ← X2Π transitions of linear FC6F+ and HC6F+, respectively. The assignment is based on the similarity of the absorption and fluorescence spectra with the A2Πg ← X2Πu electronic system of linear HC6H+ as well as the theoretically calculated vibrational and electronic excitation energies of the FC6F+ and HC6F+

The C̃2B3u ← X̃2B2g electronic absorption spectrum of butatriene cation in a neon matrix

The 2B3u ← 2B2g electronic absorption of butatriene cation (BT+) has been observed in a 6 K neon matrix. The origin band lies at 511.9 nm. The electronic transition assignment is based on comparison with the photoelectron spectrum of butatriene and the vibrational frequencies of BT+ calculated with the CASPT2 (5, 6) method. Three vibrational modes of energy 207, 511 and 813 cm−1, with their overtones and combinations, are active in the 2B3u state of BT+. It is shown that the emission observed from a glow discharge of 2-butyne at 491 nm and attributed to the origin band of this electronic transition [1] of BT+ is due to another species, because the difference of 850 cm−1 to the absorption spectrum is too large. No fluorescence of BT+ was detected in the matrix and it is expected that the 2B3u electronic state relaxes non-radiatively on a fs time scale

Electronic absorption spectra of linear C6Br and C6Br+ in neon matrices

Electronic absorption spectra of linear C6Br+ and C6Br have been recorded in 6 K neon matrices. Two strong absorption systems starting at 555.1 nm and 539.3 nm are assigned to the 1 2Π ← X 2Π electronic transition of C6Br, and 1 3Σ− ← X 3Σ− of C6Br+. Excitation of normal modes along with overtones and combination bands in the excited electronic state are observed. Assignments are based on mass-selection, photobleaching behavior, comparison with the known electronic transitions of linear C6Cl and C6Cl+, and excitation energies obtained with CASPT2 and SAC-CI theory as well as on computed vibrational frequencies

Electronic Transitions of C5H3+ and C5H3: Neon Matrix and CASPT2 Studies

Two absorption systems of C5H3+ starting at 350 and 345 nm were detected following mass-selective deposition of m/e = 63 ions in a 6 K neon matrix. These are assigned to the 1 1A1 ← X 1A1 electronic transition of 1,2,3,4-pentatetraenylium H2CCCCCH+ (isomer B+) and 1 1B2 ← X 1A1 of penta-1,4-diyne-3-ylium HCCCHCCH+ (C+). The absorptions of neutral C5H3 isomers with onsets at 434.5, 398.3, 369.0, and 267.3 nm are also detected. The first two systems are assigned to the 1 2B1 ← X 2B1 and 1 2A2 ← X 2B1 transitions of isomer B and C, respectively, and the latter two to ethynylcyclopropenyl (A) and 3-vinylidenecycloprop-1-enyl (D) radicals. The structural assignments are based on the adiabatic excitation energies calculated with the MS-CASPT2 method. A vibrational analysis of the electronic spectra, based on the calculated harmonic frequencies, supports this

Electronic Transitions of C₆H₄⁺ Isomers: Neon Matrix and Theoretical Studies

Three open-chain isomers of C₆H₄⁺ and two cyclic ones were detected following mass-selective trapping in 6 K neon matrixes. The open-chain cations 5-hexene-1,3-diyne (CH₂CH–CC–CC–H)⁺ and <i>cis-</i> (<i>cis</i>-HCC–CHCH–CCH)⁺ and <i>trans</i>-3-hexene-1,5-diyne (<i>trans</i>-HCC–CHCH–CCH)⁺, possess two absorption systems commencing at 609 and 373, 622 and 385, and 585 and 373 nm, respectively. They are assigned to the <b>1</b> ²A″ and <b>2</b> ²A″ ← X̃ ²A″, <b>1</b>²A₂ and <b>2</b> ²A₂ ← X̃ ²B₁, and <b>1</b> ²B_g and <b>2</b> ²B_g ← X̃ ²A_u electronic transitions of these cations. Two overlapping systems are detected at around 420 nm and tentatively assigned to the <b>1</b> ²A″ ← X̃ ²A″ electronic transitions of propargyl cyclopropene and <b>2</b> ²B₁ ← X̃ ²A₂ of <i>o</i>-benzyne cation structures. The assignment of the electronic transitions is based on theoretical vertical excitation energies calculated with CASPT2 and EOMEE-CCSDT methods for 12 isomers of C₆H₄⁺. These have been carried out at the geometries optimized using several ab initio methods. Adiabatic excitation energies were calculated for the five identified isomers of C₆H₄⁺

Electronic Transitions of C6H4+ Isomers: Neon Matrix and Theoretical Studies

Three open-chain isomers of C6H4+ and two cyclic ones were detected following mass-selective trapping in 6 K neon matrixes. The open-chain cations 5-hexene-1,3-diyne (CH2═CH–CC–CC–H)+ and cis- (cis-HCC–CH═CH–CCH)+ and trans-3-hexene-1,5-diyne (trans-HCC–CH═CH–CCH)+, possess two absorption systems commencing at 609 and 373, 622 and 385, and 585 and 373 nm, respectively. They are assigned to the 1 2A″ and 2 2A″ ← X̃ 2A″, 12A2 and 2 2A2 ← X̃ 2B1, and 1 2Bg and 2 2Bg ← X̃ 2Au electronic transitions of these cations. Two overlapping systems are detected at around 420 nm and tentatively assigned to the 1 2A″ ← X̃ 2A″ electronic transitions of propargyl cyclopropene and 2 2B1 ← X̃ 2A2 of o-benzyne cation structures. The assignment of the electronic transitions is based on theoretical vertical excitation energies calculated with CASPT2 and EOMEE-CCSDT methods for 12 isomers of C6H4+. These have been carried out at the geometries optimized using several ab initio methods. Adiabatic excitation energies were calculated for the five identified isomers of C6H4+