The spectrum of CH ₂ 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 b̃ B11 ã A11 electronic spectrum of the radical. In three of the four bands studied, the lower state is the bend excited, 2″ =1, level of the ã state and two of the upper levels lie below the energy of the degenerate linear configuration of the b̃ ã pair. Together with previously measured data pertaining to 2″ =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 X̃ B13 rovibrational levels, such as are known to occur in the ã A11, 2″ =0 level have not been found in 2″ =1. Absorption lines due to the predominantly triplet X̃ (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 b̃ (0,0,0)2, ã (0,7,0)1, b̃ (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.