Analysis of CH2 ã 1A1 (1,0,0) and (0,0,1) Coriolis-coupled states, ã 1A1-X∼ 3B1 spin-orbit coupling, and the equilibrium structure of CH2 ã 1A1 state

The symmetric and antisymmetric stretch spectra of ã ¹A₁ CH₂ are measured with Doppler-limited resolution by infrared flash-kinetic spectroscopy between 2600 and 3050 cm^-1. The spectra are significantly perturbed by spin-orbit interactions between near-resonant levels of X∼ ³B₁ in both lower and upper levels of the transitions, and by Coriolis interaction between symmetric and antisymmetric stretch states. The triplet character of the perturbed levels is detected by observing broadening of M_J structure in a magnetic field of about 1 kG. The levels that are likely to be perturbed by triplet methylene are identified using the experimentally observed and theoretically calculated ³B₁ energy level structure. The term values of the remaining symmetric and antisymmetric stretch levels are simultaneously fit to Watson's Hamiltonian including Coriolis coupling. This analysis provides the remaining information needed to determine the equilibrium rotational constants [A_e =19.8054(206), B_e=11.2489(45), and C_e =7.2386(36) cm^-1 ], and, therefore, the equilibrium structure (r_e=1.107 Å, and θ_e =102.4°) of this fundamentally important carbene. The experimental and theoretical structures are in good agreement.