Photochemistry of deuterated acetylketenes: Matrix isolation infrared spectroscopic and ab initio studies

The partially deuterated s-Z and s-E conformers of acetylketene (1 and 2) were generated by flash vacuum pyrolysis of two different deuterated precursors, 3 and 4. The conformer mixture was characterized by low-temperature FTIR spectroscopy in Ar, N-2, and Xe matrices. The observed frequencies and intensities are in excellent agreement with ab initio calculations at the MP2/6-31G* and B-LYP/6-31G* levels. Irradiation of Ar matrices in the UV (313 nm) caused the appearance of new sets of absorptions, which disappeared upon annealing of the matrices to 35 K. Difference spectra revealed no new absorptions due to OD bands arising from photoisomers 7-10, thereby rigorously proving that no C-D/O-D tautomerism takes place and that the new absorptions observed are due to exceptionally prominent photochemically populated matrix sites.