Knowledge Bank

The rotationally resolved nonresonant two-photon mass analyzed threshold ionization (MATI) spectra and zero kinetic energy (ZEKE) photoelectron spectra of $CH2CO+$ and $CD2CO+$ are presented. The MATI and ZEKE spectra of $CH2CO+$ are dominated by the totally symmetric modes $\nu u(C=Cstretch)$ and $\nu u(C=Ostretch)$, with weaker excitation of $\nu 3(CH2scissor)$, while those of $CD2CO+$ are dominated by approximately equally intense $\nu 2,\nu 3$, and $\nu 4$. This is consistent with the theoretical calculations of Takeshita, which indicate a strong coupling of $\nu 3$ and $\nu 4$ modes of $CD2CO+$ in the ground state. In addition, weak excitations to the nontotally symmetric vibrations $\nu 5(CH2wag),\nu 6$ (C=C=O linear bend) and $\nu 9$ (C=C=O linear bend) are also observed in the MATI spectra of both isotopomers. Rotational structure is dominated by very strong $\Delta Ka=\pm 1$ manifolds with two orders of magnitude weaker $\Delta Ka=+3$ features. Analysis of the ZEKE spectra provides the ionization potentials ($77538.8\pm 2cm-1$ for $CH2CO$ and $77533.7\pm 2cm-1$ for $CD2CO$) and rotational constants for the ground states of both ketene cations.