OXALYL HALIDES - ANALYSIS OF 3680 A ABSORPTION SYSTEM OF OXALYL CHLORIDE

The vapor-phase absorption spectrum of oxalyl chloride in the 4000-3000 Å region has been examined under high resolution. The bands are sharp in the region of the system origin, which is at 27 188.9 cm-1, chlorine-isotope splittings being resolved. Excited state progressions in ν′1 (1460 cm-1), ν′4 (398.5 cm-1) and ν′5 (281.8 cm-1) have been identified; other assignments are ν′2 = 970 cm-1 and ν′3 = 619.2 cm-1, For the ground state, ν″1-ν″5 = 1783.3, 1217.1, 612.1, 498.5 and 283.0 cm-1, respectively. Bands in which these totally-symmetric vibrations are excited are accompanied by sequences in +78 cm-1 (ν7 sequence), -12 cm-1 (ν12 sequence), +32 cm-1 and -84 cm-1, the latter sequences being tentatively identified as in ν6 and ν11, respectively. The band structure and intensity distribution is consistent with an allowed electronic transition from a planar trans ground state to a similar excited state in which r(CO) has increased by ∼0.08 Å, r(CC) has decreased, and the CCO angle has opened slightly. The transition is identified as A ̃1Au- X ̃1Ag under the C2h point group, the upper state resulting from n → π* electron promotion. © 1968.