Multiphoton ionization mass spectroscopy of deuterated analogs of acetaldehyde: Evidence for deuterium scrambling

Fragmentation patterns as a function of laser flux are obtained for CD3CHO using a quadrupole mass spectrometer for excitation at the origin of the two-photon resonant n→3s Rydberg transition at 55 138 cm−1. Extensive fragmentation is found with product ion branching ratios showing a strong dependence on laser flux. Fragments such as CDO+ appear, indicating that bond rearrangement occurs. In the case of the CD+3, CD2H+ ion pair, the CD2H+ scrambled product dominates, although in no case does the scrambling reach the statistical limit obtained by assuming that all hydrogen species are equivalent. The individual ion signal data can be fit with a rate equation model. Isotopic selectivity for mixtures of CD3CDO/CH3CHO is demonstrated; no partially deuterated products are found, indicating that the scrambling in CD3CHO is not collisionally induced.