A refined potential surface for the X̃ 3B1 electronic state of methylene CH2

In this paper we use the nonrigid bender Hamiltonian to calculate the rotation–vibration energy levels of 12CH2, 12CD2, and 13CH2 in the X 3B1 ground state. We adjust the shape of the potential surface used in the calculation in order to optimize the fit of the calculated energy level separations to the 61 available experimental values for these three isotopes of methylene. In the fit we vary nine parameters and determine, among other things, that the equilibrium bond length is 1.0748±0.0004 A, the equilibrium bond angle is 133.84°±0.05°, the height of the barrier to linearity is 1940±80 cm−1, and the optimum bond length for the molecule when it is linear, at the saddle point in the potential surface, is 1.060±0.005 A. From our results we predict the stretching frequencies in 12CH2 to be ν1=2950±40 cm−1 and ν3=3080±40 cm−1.