Abstract

An analysis of the ${\tilde{\text{b}}}^1 {\text{B}}_1-{\tilde{\text{a}}}^1 {\text{A}}_1$ 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 ${\tilde{\text{X}}}^3 {\text{B}}_1$ state and correlate with a degenerate ${}^1{\Delta }_g$ state at the linear configuration of the molecule. This degeneracy leads to extreme complexity in the spectrum. The $\tilde{\text{a}}$ and $\tilde{\text{b}}$ 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 $\tilde{\text{a}}$ state. Although the visible region of the $\tilde{\text{b}}-\tilde{\text{a}}$ 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.

© 1995 Optical Society of America