Action infrared spectroscopy of H2COH+ and H2COD+: Experimental and theoretical aspects

We report the first infrared spectra of deuteronated formaldehyde, H2COD+, together with extended data for H2COH+, obtained by combining Ne-tagging infrared predissociation (IRPD) and leak-out spectroscopy (LOS). Broadband spectra were recorded using the FELion cryogenic ion-trap coupled to the infrared free electron lasers at HFML-FELIX and compared with high-level quantum-chemical predictions. Vibrational band centers and intensities were computed using vibrational configuration interaction (VCI) and rovibrational spectra simulations were based on VCI combined with spectroscopic parameters from composite schemes rooted in the coupled-cluster theory. Band positions match VCI predictions, while shapes and relative intensities exhibit mode-dependent differences between IRPD and LOS.