Analysis of the laser photoelectron spectrum of CH⁻₂

We have simulated the photoelectron spectrum of CH⁻₂ using the model described previously [Sears and Bunker, J. Chem. Phys. 79, 5265 (1983)]. The optimization of the fit of the simulated spectrum to the recently observed spectrum of Lineberger and co‐workers [J. Chem. Phys. 81, 1048 (1984) and preceding paper] has enabled us to determine the rotation‐bending energy levels of triplet CH₂ over an energy range of more than 1 eV. It has also enabled us to determine that the rotational temperature of the CH⁻₂ in the experiment is 220 K and that, for v₂=1, the vibrational temperature is 680 K. For CH⁻₂ we determine that a_e=103° and that ν₂=1230 cm⁻¹. The singlet–triplet splitting in methylene is determined to be 3150±30 cm⁻¹ (0.3905±0.004 eV, 9.01±0.09 kcal/mol) from the photoelectron spectrum, in excellent agreement with the more accurate value previously obtained from LMR spectroscopy [McKellar et al., J. Chem. Phys. 79, 5251 (1983)] of 3165±20 cm⁻¹ (0.3924±0.0025 eV, 9.05±0.06 kcal/mol), and the electron affinity of triplet CH₂ is determined to be 0.652±0.006 eV.