Gas phase electronic spectrum of linear AlCCH

Abstract

The electronic spectrum of the aluminium containing species AlCCH has been detected in the gas phase in the region 315–355 nm. The experiment used a mass selective resonant two-color two-photon ionization technique coupled to a laser ablation source. Structures of the AlCCH isomers have been optimized using density functional theory (DFT) and the excitation energies to the low-lying electronic excited states calculated. Based on the analysis of the observed rotational structure and the theoretical data, the spectrum is assigned to the A ¹Π ← X ¹Σ⁺ electronic transition of linear AlCCH. The vibronic band system is complicated by the Renner–Teller effect in the excited state. The assignment yields ν₄″ = 516.4 cm⁻¹ for the stretching mode in the ground X ¹Σ⁺ state and ν₄′ = 654.5 cm⁻¹ for A ¹Π excited state. Molecular constants determined from the rotational analysis are B₀″ = 0.16487(14), B₀′ = 0.17845(13) and T₀ = 28 755.04 cm⁻¹. The experimental and theoretical data indicate a shorter Al–C bond in the A ¹Π excited than the X ¹Σ⁺ ground state.