Analytic Morse/long-range potential energy surfaces and predicted infrared spectra for CO_2 - H_2

摘要

Five-dimensional ab initio potential energy surfaces (PESs) for CO _2 - H_2 that explicitly incorporate dependence on the Q_3 asymmetric-stretch normal-mode coordinate of the CO_2 monomer and are parametrically dependent on its Q_1 symmetric-stretch coordinate have been calculated. Analytic four-dimensional PESs are obtained by least-squares fitting vibrationally averaged interaction energies for v _3 (CO_2) =0, and 1 to the Morse/long-range potential function form. These fits to 23 113 points have root-mean-square (rms) deviations of 0.143 and 0.136 cm~(-1), and require only 167 parameters. The resulting vibrationally averaged PESs provide good representations of the experimental infrared data: for infrared transitions of para- and ortho- H _2 - CO_2, the rms discrepancies are only 0.004 and 0.005 cm~(-1), respectively. The calculated infrared band origin shifts associated with the _3 fundamental of CO_2 are -0.179 and -0.092 cm~(-1) for para- H_2 - CO_2 and ortho- H_2 - CO_2, in good agreement with the (extrapolated) experimental values of -0.198 and -0.096 cm~(-1).