HCl Elimination from Ethanesulfenyl Chloride and Chlorodimethyl SulfideThioacetaldehyde (5) is prepared by matrix photolysis of ethanesulfenyl chloride (3) or thiirane (4) and by flash pyrolysis of allyl ethyl sulfide (6). Matrix irradiation of3or5with 222‐nm light results in a dehydrogenation, and a mixture of thiirene (7), ethynethiol (8), and thioketene (9) is formed. Flash pyrolysis of chlorodimethyl sulfide (1) yields ethenethiol (11) together with thiirane (4), whereas ethanesulfenyl chloride (2) gives ethene under the same conditions. The identification of thioacetaldehyde (5) is based on the comparison between the experimental and calculated IR spectr