Theoretical study of the dipole moment function of OH(X 2Π)

Abstract

The convergence of the electric dipole moment function for the X ²Π state of OH is studied as a function of extensions of both the one‐particle and n‐particle basis sets. Full configuration‐interaction (FCI) energies and dipole moments in both [4s3p1d/2s1p] and [4s3p2d/2s1p] Gaussian basis sets are used for the calibration of a variety of approximate methods of including electron correlation. A CASSCF/MRSDCI treatment, which accurately reproduces the FCI potential and dipole moment function, is then performed in an extended [6s5p4d2f1g/4s3p2d] one‐particle basis set. The dipole moment is evaluated both as an expectation value and as an energy derivative. The energy derivative is found to be generally superior, especially for the coupled pair functional approaches. Our best dipole moment function gives a permanent dipole moment within 0.01 D of experiment for v=0, and within 10% of the accurate experimental value for the difference in dipole moments between v=0 and v=1. However, our theoretical value for v=2 does not lie within the experimental error bounds.