Rotational excitation of singly and doubly deuterated formaldehyde induced by collisions with molecular hydrogen. Rate coefficients and pressure broadening

This work presents calculations of state-to-state collisional rate coefficients for the rotational excitation of the deuterated formaldehyde isotopologs, HDCO and =0) and =1). These calculations are based on the induced by collisions with molecular hydrogen, coupled with experimental verification by pressure-broadening measurements. Time-independent scattering calculations were performed using the close-coupling method to compute inelastic cross sections for collisions with both (j_ 2 (j_ 2 potential energy surface previously determined at the CCSD (T) level of theory and transformed to account for the isotopic substitution. The resulting rate coefficients cover the lowest 100 rotational states of HDCO and 60 states of and with internal energies less than 200 ̧m. Collisional data were obtained for temperatures up to 100 K for HDCO and and extended up to 300 K using the coupled-states approximation. The computed rate coefficients show systematic differences between and collisions, with the former generally yielding larger values by a factor of 2--3. Rate coefficients for HDCO--̋H are found to be lower by a factor of 2 to 3 compared to those of and Pressure-broadening coefficients were also calculated using the random-phase approximation and compared with new laboratory measurements, yielding agreement by about 5--30%.