Molecular orbital anharmonic estimates for the infrared spectrum of CO2

On the ν1/2 ν2 Resonance in the Complex of Carbon Dioxide with Dimethyl Ether

“…Values of the harmonic frequencies and higher order force constants used in the calculations have been collected in Table 1. The values of the cubic force constants k 1,i,i in Table 1 are close to the experimental, as well as ab initio values at various levels for monomer CO 2 , [28,29] showing that the influence of the complexation of these force constants is very limited. The calculated eigenvalues of the perturbation matrices are compared with the observed frequencies in Table 2.…”

Vibrational Energy Levels via Finite-Basis Calculations Using a Quasi-Analytic Form of the Kinetic Energy

“…The isotopologue 12 C 16 O 2 and some others were extensively studied experimentally; as a result of that it was possible to experimentally infer quartic and sextic − force fields for this species. Ab initio calculations of the quartic force field of 12 C 16 O 2 have been carried out at different levels of theory. − Recently, Rodriguez-Garcia et al calculated the PES of 12 C 16 O 2 from a set of energy points computed using coupled-cluster methods with partial and full inclusion of triple excitation effects together with correlation-consistent basis sets and an extrapolation technique to converge to the basis set limit. They presented the PES in terms of a fourth-order Taylor expansion and by means of numerical values on a Gauss−Hermite quadrature grid.…”

“…Concerning the prediction of the vibrational spectrum, most theoretical studies were based on vibrational perturbation theory in second order (VPT2), − and fundamental transitions were the main focus of interest. ZPE and 13 vibrational states in the range of 2000−4900 cm −1 were calculated within DVR using different quartic and sextic force fields ,, and a Hamiltonian expressed in terms of orthogonal Jacobi and Radau coordinates .…”