Accurate analytic potential energy function and spectroscopic study for CH( X2Π) radical using coupled-cluster theory in combination with the correlation-consistent quintuple basis set

The coupled-cluster singles-doubles-approximate-triples [CCSD(T)] theory in combination with the correlation-consistent quintuple basis set (aug-cc-pV5Z) is used to investigate the spectroscopic properties of the CH (X-2 Pi) radical. The accurate adiabatic potential energy curve is calculated over the internuclear separation ranging from 0.07 to 2.45 nm and is fitted to the analytic Murrell-Sorbie function, which is employed to determine the spectroscopic parameters, omega(eZe), alpha(e), and B-e. The present D-e, R-e, omega(e), omega(eZe), alpha(e) and B-e values are of 3.6261 eV, 0.11199 nm, 2856.312 cm(-1), 64.9321 cm(-1), 0.5452 cm(-1) and 14.457 cm(-1), respectively. Excellent agreement is obtained when they are compared with the available measurements. With the potential obtained at the CCSD(T)/aug-cc-pV5Z level of theory, a total of 18 vibrational states is predicted when J=0 by numerically solving the radial Schrodinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced for the CH (X-2 Pi) radical when J=0 for the first time, which are in good agreement with the available RKR data. (C) 2008 Elsevier B.V. All rights reserved.