Laser-induced fluorescence of trapped molecular ions: the CH+A1Πâ†�X1Σ+ system

Abstract

The CH⁺ and CD⁺A¹Πâ†�X¹Σ⁺ absorption spectra have been obtained by laser excitation of these fragment ions. The ions are contained in a mass-selective quadrupole ion trap under collision-free conditions. The spectra therefore reflect the nascent internal-energy distributions of the ions, which were produced by electron impact on CH₄(CD₄) or C₂H₂(C₂D₂). Both parent gases gave virtually identical spectra; large rotational and vibrational excitation was observed. The equipment was also capable of measuring the radiative lifetime of CH⁺(CD⁺)A²Π(v= 0), and the measured value, 815 ns, is found to be in good agreement with theoretical calculations of this quantity.