The formaldehyde cation: Rovibrational energy level structure and Coriolis interaction near the adiabatic ionization threshold

Abstract Rotationally resolved pulsed-field-ionization zero-kinetic-energy photoelectron spectra of the 0 0 , 6 1 and 4 1 vibrational levels of the X ∼ + 2 B 2 ground electronic state of the formaldehyde cation were recorded using a resonant three-color three-photon excitation scheme. The first adiabatic ionization energy of CH 2 O (87793.33(1.30) cm −1 ) and the rigid-rotor rotational constants ( A +  = 8.874(8) cm −1 , B +  = 1.342(15) cm −1 , C +  = 1.148(18) cm −1 ) of the vibronic ground state of CH 2 O + were derived. A strong a -type Coriolis interaction between the 6 1 and 4 1 vibrational levels was observed. The Coriolis coupling parameter ξ 4 , 6 a and the deperturbed fundamental vibrational frequencies of the in-plane-rocking mode ν 6 and the out-of-plane bending mode ν 4 were determined to be 8.70(10) cm −1 , 823.67(30) cm −1 and 1036.50(30) cm −1 , respectively. The intensity distribution of the photoelectron spectra was analyzed in the realm of a simple photoionization model.