The spectrum of CH2 near 1.36 and 0.92 μm: Reevaluation of rotational level structure and perturbations in ã(010).

The spectrum of methylene in the 1.3–1.4 and 0.89–0.94 μm wavelength regions has been recorded in absorption using frequency-modulated cw diode and Ti:sapphire laser sources. The spectral lines have Doppler-limited resolution and have been assigned to bands in the b ¹B₁←ã ¹A₁ electronic spectrum of the radical. In three of the four bands studied, the lower state is the bend excited, υ₂^″=1, level of the ã state and two of the upper levels lie below the energy of the degenerate linear configuration of the b/ã pair. Together with previously measured data pertaining to υ₂^″=1, the data have been used to refine the precision of the experimentally determined rotational structure in this level. Although several K^″=1 levels do show shifts of more than 0.1–0.2 cm^-1, multiple strong perturbations due to near-resonant background X ³B₁ rovibrational levels, such as are known to occur in the ã ¹A₁, υ₂^″=0 level have not been found in υ₂^″=1. Absorption lines due to the predominantly triplet X(040) 4₁₄ level, responsible for most of the perturbation of ã(010) 5₁₅, have been identified in the spectra. The data also fix the energies of the b(0,0,0)², ã(0,7,0)¹, b(0,2,0)³, and ã(0,10,0)² upper vibronic levels, where the numbers in parentheses are the vibrational quantum numbers with superscript K, the projection of the total angular momentum on the a-inertial axis. [ABSTRACT FROM AUTHOR]