A CORRELATED AB-INITIO STUDY OF THE (X)OVER-TILDE(2)A(1) AND (A)OVER-TILDE(2)E STATES OF MGCH3

The (X) over tilde (2)A(1) and (A) over tilde (2)E states of the MgCH3 radical have been studied with correlation consistent basis sets and the coupled cluster method RCCSD(T) in order to compare with two recen t experimental efforts [M. A. Anderson and L. M. Ziurys, Astrophys. J. 452, L157 (1995); R. Rubino, J. M. Williamson, and T. A. Miller, J. C hem. Phys. 103, 5964 (1995)]. The best computed values [RCCSD(T)/cc-pC VTZ] for the (X) over tilde (2)A(1) state are (experimental results in parentheses): A(e) = 160.433 GHz, B-e = 10.948 GHz (B-0 = 11.008 GHz) , and mu(e) = 1.011 D. The Mg-CH3 bond is weak, 26.3 kcal/mol. Values for the (A) over tilde (2)E state are A(e) = 154.648 GHz (A(0) = 149.6 66 GHz), B-e = 10.87 GHz (B-0 = 10.932 GHz), and mu(e) = 1.022 D. The excitation energy (T-e) for the (A) over tilde (2)E <-- (X) over tilde (2)A(1) transition is 19 999 cm(-1) (T-00 = 20 030 cm(-1)). A brief d iscussion of bonding trends in Mg-containing radials is included. (C) 1996 American Institute of Physics.