Rotation-vibration energy level clustering in the X∼2B1 ground electronic state of PH2

We use previously determined potential energy surfaces for the Renner-coupled X∼2B1 and A∼2A1 electronic states of the phosphino (PH2) free radical in a calculation of the energies and wavefunctions of highly excited rotational and vibrational energy levels of the X∼ state. We show how spin-orbit coupling, the Renner effect, rotational excitation, and vibrational excitation affect the clustered energy level patterns that occur. We consider both 4-fold rotational energy level clustering caused by centrifugal distortion, and vibrational energy level pairing caused by local mode behaviour. We also calculate ab initio dipole moment surfaces for the X∼ and A∼ states, and the X∼-A∼ transition moment surface, in order to obtain spectral intensities.