The initial oxidation product of dimethyl sulfide in the marine boundary layer, the methyl thiomethyl radical, has remained elusive. A structurally analogous biradical with one radical center in the alpha-position to a sulfur atom could now be obtained by UV irradiation of p-nitrobenzaldehyde dithiane isolated in solid dinitrogen (N-2) or Ar at cryogenic temperatures. A spin-forbidden reaction with triplet dioxygen (O-3(2)) does not occur. The dithiane of o-nitrobenzaldehyde rather undergoes a series of rearrangements under the same conditions, resulting in overall photodeprotection.