A reinterpretation of the CH−2 photoelectron spectrum

Abstract

We simulate the photoelectron spectrum of CH⁻₂ using the known bending potential functions of CH₂ in the X̃ ³B₁ and ã ¹A₁ states, together with a bending potential function and temperature for CH⁻₂ in the X̃ ²B₁ state that are adjusted in order to fit the experimental spectrum. We find that in order to reproduce the spectrum we must have a CH⁻₂ temperature of about 2500 K and a singlet–triplet separation in CH₂ of 3250±200 cm⁻¹ (0.40±0.02 eV or 9.3±0.6 kcal/mol). This leads to a value for the electron affinity of X̃ state CH₂ of 0.65±0.02 eV. In the simulation we include rotational levels with J (or N) up to 20, which means that over 500 000 rovibronic transitions are involved.