THE DIPOLE-MOMENT AND MAGNETIC HYPERFINE PROPERTIES OF THE EXCITED A(2)SIGMA(+)(3S-SIGMA) RYDBERG STATE OF NITRIC-OXIDE

The dipole moment and magnetic hyperfine properties of the A (2) Sigma(+) Rydberg state of nitric oxide have been evaluated at a variety of levels of theory with extended correlation consistent basis sets. Using the finite field approach to compute the dipole moment, restricted coupled cluster RCCSD(T) and complete active space-configuration interaction CAS-CI+Q methods yield values (1.09-1.12 D) that are essentially identical to experiment. In contrast, dipole moments computed as an expectation value of the dipole moment operator typically differ from experiment by 0.1-0.6 D. The rather unfavorable comparisons with experiment reported in previous theoretical studies may stem, in part, from the method chosen to evaluate the dipole moment. Magnetic hyperfine properties were evaluated using a variety of unrestricted and restricted open-shell Martree-Fock-based methods. We estimated the full CI limiting properties by exploiting the convergence behavior of a sequence of MRCI wave functions. The isotropic component A(iso)(N-14) of 39+/-1 MHz evaluated in this fashion is in excellent accord with the experimental value of 41.4+/-1.7 MHz. Highly correlated UHF-based methods [e.g., CCSD(T) and QCISD(T)] yield comparable values of 40-41 MHz that are in good agreement with both experiment and the apparent full CI limit. However, for A(iso)(O-17), the full CI limit (-97+/-2 MHz) and the UHF-based results (ca.-118 MHz) differ by roughly 20 MHz. It remains unclear how to reconcile this large discrepancy. (C) 1995 American Institute of Physics.