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

Abstract

In this paper we use the nonrigid bender Hamiltonian to calculate the rotation–vibration energy levels of ¹²CH₂, ¹²CD₂, and ¹³CH₂ in the X̃ 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 Å, 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 Å. From our results we predict the stretching frequencies in ¹²CH₂ to be ν₁=2950±40 cm⁻¹ and ν₃=3080±40 cm⁻¹.