Oxalyl halides: Analysis of the 3870 Å absorption system of oxalyl chloridefluoride

Oxalyl chloridefluoride, (COCl) (COF), exhibits a very weak discrete absorption system in the region 3500–3900 Å. This system, the 3870 Å system, appears at vapor absorption pressure-paths of ～1 m atm, and merges into the much stronger 3480 Å absorption system to shorter wavelengths. The bands of the 3870 Å system have a linelike appearance under the highest resolution available, so that isotopic splittings could be used extensively as an aid to vibrational analysis. Because of the reduced symmetry of the molecule as compared to (COX)₂ species, additional vibrations are active as compared to n → π transitions of the latter; but the same type of vibrations are responsible for the band structure, namely, carbonyl stretching modes and in-plane rocking and bending modes of the two halves of the molecule. All of the stronger bands belong to one electronic transition, with origin at 25 828.7 cm^?1, which is assigned as $\text{a}\text{?}{}^3\text{A′ -}\text{X}\text{?}{}^1\text{A′}$ of the trans-molecule, produced by $\text{n → π}{}^1$ electron promotion. Only small geometric changes occur upon electronic excitation.