Spectroscopic Investigations on AlH(X1Σ+) Radical Using Multireference Configuration Interaction Theory in Combination With Correlation-Consistent Quintuple Basis Set Augmented With Diffuse Functions

The equilibrium internuclear separations, harmonic frequencies, and potential energy curves (PECs) of the AlH(X-1 Sigma(+)) radical have been investigated using the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in combination with a series of correlation-consistent basis sets in the valence range. The PECs are all fitted to the Murrell-Sorbie function, which are used to reproduce the spectroscopic parameters (D-e, D-0, omega(e)chi(e), alpha(e), and B-e). By comparison with the available experimental results, the PEC obtained at the basis set, aug-cc-pV5Z, is selected to investigate the vibrational manifolds. The present D-0, D-e, R-e, omega(e), omega(e)chi(e), alpha(e), and Be are of 3.0731 eV, 3.1775 eV, 0.16510 nm, 1683.37 cm(-1), 29.3786 cm(-1), 0.18876 cm(-1), and 6.3663 cm(-1), respectively, which almost perfectly conform to the available measurements. With the potential determined at the MRCI/aug-cc-pV5Z level of theory, the total of 26 vibrational states is predicted when the rotational quantum number J is set to equal zero (J = 0) by numerically solving the radial Schrodinger equation of nuclear motion with the Numerov method. The complete vibrational levels, classical turning points, inertial rotation, and centrifugal distortion constants are determined when J = 0 for the first time, which are in excellent agreement with the available experimental data. (C) 2009 Wiley Periodicals, Inc. Int J Quantum Chem 111: 554-562, 2011