| Abstract | Rotationally resolved nonresonant two-photon mass analyzed threshold ionization (MATI) and zero kinetic energy (ZEKE) photoelectron spectra of CH2CO+ and CD2CO+ are reported. The spectra are dominated by the origin band and totally symmetric a1 vibrations, ν4 (C=C symmetric stretch) and ν2 (C=O asymmetric stretch) for CH2CO+, and ν1 (C=O asymmetric stretch), ν3 (C=C symmetric stretch), and ν4 (CD2 scissor) for CD2CO+. In addition, several weaker bands are observed in the MATI spectra: ν3 (CH2 scissor) in CH2CO+; b1 vibrations ν5 and ν6 (C=C=O linear bend and CH2 wag) in both isotopomers; b2 vibration ν8 (CD2 rock) for CD2CO+; b2 vibration ν9 (C=C=O linear bend) for CH2CO+; as well as overtones and combination bands. Rotational structure of the origin band is dominated by three very strong ΔKa=±1 bands with 2 orders of magnitude weaker ΔKa=+3 bands. A similar ΔKa=±1 three-band pattern is observed for the a 1 vibrational modes. For the b1 modes a single-band pattern resulting from the ΔKa=0 selection rule is present. Fundamental wave numbers for six vibrational modes of CH2CO+ and seven modes of CD2CO+ are determined. Rotational analysis of the partially resolved ZEKE spectra yields the ionization potentials (77539.4±2.0 cm−1 for CH2CO and 77534.3±2.0 cm−1 for CD2CO) and rotational constants for the ground states of both ketene cations. |
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