Photofragment spectroscopy of FeCH2+, CoCH2+, and NiCH2+ near the M+-CH2 dissociation threshold

Photofragment spectra of jet-cooled MCH2+ (M = Fe, Co, Ni) have been measur ed. Our investigation of NiCH2+ represents the first reported spectroscopic study of this molecule. A spectroscopic threshold is observed for each of the three systems. In addition to imposing strict upper limits on the M+-CH 2 bond strengths, these results further the discussion concerning the inter pretation of spectroscopic thresholds as thermodynamic limits. The measured upper limits are: D degrees(0)(Fe+-CH2) less than or equal to 342 +/- 2 kJ /mol, D degrees(0)(Co+-CH2) less than or equal to 331 +/- 2 kJ/ mel, and D degrees(0)(Ni+-CH2) less than or equal to 295 +/- 5 kJ/mol. Three distinct, 2-nm-wide peaks are observed in the photofragment spectrum of CoCH2+, but the spectra lack sharp structure above threshold.