Rovibrational energy level structure of the X̃ 2B1 ground electronic state of CH2CO+ and CD2CO+

Rotationally resolved pulsed-field-ionization zero-kinetic-energy (PFI-ZEKE) photoelectron spectra of the X̃ 2B1←X̃ 1A1 transition of CH2CO and CD2CO have been recorded between 77 400 and 79 900 cm−1. The first adiabatic ionization potentials (IP(CH2CO)=77 538.7±0.7 cm−1, IP(CD2CO)=77 533.4±0.7 cm−1), ionic rotational constants and vibrational energies have been derived for both isotopomers from the dominant vibrational bands. The vibrational structure of the cation is subject to several perturbations that are discussed in the light of ab initio calculations. The analysis of the rotational structure and of photoionization selection rules provides new information on the VUV photoionization dynamics of ketene.