An ab initio calculation of the rotation-vibration energies of singlet and triplet NH₂⁺ using the morbid Hamiltonian

For the X̃ 3B1, ã1A1 and b̃ 1B1 electronic states of the NH2+ molecular ion we have calculated ab initio points on the potential energy surfaces using a complete second-order configuration interaction calculation for the six valence electrons. For the X̃ and ã states the rotation-vibration energies were calculated from these surfaces using the MORBID Hamiltonian. For the X̃ state we obtain re = 1.0338 Å, αe = 153.17°, and a barrier to linearity of only 209 cm-1. Our best estimate for the vibrational frequencies are ν1 = 3118 cm-1, ν2 = 918 cm-1 and ν3 = 3363 cm-1. For the ã state we obtain re = 1.0510 Å, αe = 108.37°, ν1 = 3027 cm-1, ν2 = 1289 cm-1, and ν3 = 3111 cm-1. © 1987.