Accurate analytic potential energy function and spectroscopic study for CH(X2Î ) 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(X2Π) 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, ωeχe, αe and Be. The present De, Re, ωe, ωeχe, αe and Be 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 Schrödinger equation of nuclear motion. The complete vibrational levels, classical turning points, inertial rotation and centrifugal distortion constants are reproduced for the CH(X2Π) radical when J = 0 for the first time, which are in good agreement with the available RKR data.