15min:

SCOTT WREN, KRISTEN M. VOGELHUBER AND W. CARL LINEBERGER, JILA, University of Colorado and National Institute of Standards and Technology, and Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309.

Dihalocarbenes of the form CX₂ (X = F, Cl, Br, I) are important intermediates in organic reactions, due to the unique chemical properties of their low-lying neutral singlet ¹A₁ and triplet ³B₁ states that affect their reactivities. Disagreement between experimental and theoretical results for the singlet-triplet splittings in CCl₂^-, CBr₂^-, and CI₂^- prompted a careful reinvestigation of the photoelectron spectra of these compounds, revealing contamination from HCX₂^- species. Contributions from contaminants previously obscuring the dihalocarbene ³B₁ triplet spectra have been minimized, and photoelectron spectra of isolated HCX₂^- compounds were collected to further elucidate the dihalocarbene experimental data. The new CCl₂^- 351 nm photoelectron spectra exhibit vibrationally resolved transitions to singlet and triplet electronic states; careful analysis drastically alters the previous identification of the triplet state origin, resulting in substantially improved agreement with high level calculations.