A Possible Reinterpretation of the Photoelectron Spectra of [CCl2]-•, [CBr2]-•, and [CI2]-•: A Role for Quartet Isodihalocarbene or Dihalocarbene Radical Anions?

Abstract

We address a discrepancy between the large singlet−triplet (S−T) splitting values computed by advanced ab initio methods for three of the dihalocarbenes CX2 (X = Cl, Br, I) and the much smaller values deduced from photoelectron spectra of CX2-• ions. Our G3 calculations lead us to propose that the band of CX2-• (X = Cl, Br, I) that is presently attributed to the 2[X−C−X]-• → 3X−C−X transition is actually due to photodetachment from a metastable species, 4[X−C−X]-• → 3X−C−X or, less likely, 4[CX−X]-• → 3[CX−X] (and, conceivably, 2[CX−X]-• → 3[CX−X]).