Laboratory detection of protonated formaldehyde (H2COH/+/)

The first spectroscopic identification of protonated formaldehyde has been made by observing the nu1 fundamental band (O-H stretch) in the 2.9-micron region with a difference-frequency laser as a radiation source. The molecular structure is confirmed to be the O-protonated form H2COH(+), in agreement with theoretical predictions. The band is found to be perturbed, and only the K(a) = 0 and K(a) = 1 lines have been assigned at the present stage. The spectroscopic parameters for the ground state, however, have been derived from the combination differences. The rotational transition frequencies useful for obtaining interstellar lines are calculated from those molecular constants. 26 refs