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

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. Usin g the finite field approach to compute the dipole moment, restricted c oupled cluster RCCSD(T) and complete active space-configuration intera ction CAS-CI+Q methods yield values (1.09-1.12 D) that are essentially identical to experiment. In contrast, dipole moments computed as an e xpectation value of the dipole moment operator typically differ from e xperiment by 0.1-0.6 D. The rather unfavorable comparisons with experi ment reported in previous theoretical studies may stem, in part, from the method chosen to evaluate the dipole moment. Magnetic hyperfine pr operties were evaluated using a variety of unrestricted and restricted open-shell Martree-Fock-based methods. We estimated the full CI limit ing properties by exploiting the convergence behavior of a sequence of MRCI wave functions. The isotropic component A(iso)(N-14) of 39+/-1 M Hz evaluated in this fashion is in excellent accord with the experimen tal 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 UH F-based results (ca.-118 MHz) differ by roughly 20 MHz. It remains unc lear how to reconcile this large discrepancy. (C) 1995 American Instit ute of Physics.