New near infrared spectra of the CH2 radical

Abstract

An analysis of the b ˜ 1   B 1 − a ˜ 1   A 1 electronic spectrum of methylene was first reported in 1966 by Herzberg and Johns.1 Since that time, numerous experimental and theoretical investigations have been carried out on this chemically important species. The two lowest singlet states in CH2 lie approximately 3000 and 12000 cm-1 above the ground X ˜ 3   B 1 state and correlate with a degenerate 1 Δ g state at the linear configuration of the molecule. This degeneracy leads to extreme complexity in the spectrum. The a ˜ and b ˜ states may be regarded as derived from a severe Renner-Teller effect in a linear singlet CH2 molecule and the resulting vibronic structure leads to a highly irregular band system, especially at energies near to that of the degenerate linear configuration, recently2 calculated to lie some 8800 cm-1 above the zero point level of the a ˜ state. Although the visible region of the b ˜ − a ˜ spectrum has been extensively studied3,4 since the original work of Herzberg and Johns, there have been no experiments reported in the near infrared region due to less efficient dye laser operation at these wavelengths.