DOE OSTI2011
Recently, we reported ab initio quartic force fields (QFFs) for the cyclic and linear forms of the C{sub 3}H{sub 3}{sup +} molecular cation, referred to as c-C{sub 3}H{sub 3}{sup +} and l-C{sub 3}H{sub 3}{sup +}. These were computed using high levels of theory. Specifically the singles and doubles coupled-cluster method that includes a perturbational estimate of connected triple excitations, CCSD(T), was used in conjunction with extrapolation to the one-particle basis set limit, and corrections for scalar relativity and core correlation were included. In the present study, we use these QFFs to compute highly accurate fundamental vibrational frequencies and other spectroscopic constants for the c-{sup 13}CC{sub 2}H{sub 3}{sup +}, c-C{sub 3}H{sub 2}D{sup +}, c-{sup 13}CC{sub 2}H{sub 2}D{sup +} isotoplogues of c-C{sub 3}H{sub 3}{sup +}, and the H{sub 2}CCCD{sup +}, HDCCCH{sup +}, H{sub 2}{sup 13}CCCH{sup +}, H{sub 2}C{sup 13}CCH{sup +}, and H{sub 2}CC{sup 13}CH{sup +} isotopologues of l-C{sub 3}H{sub 3}{sup +}. Improvements in ab intitio methods have now made it possible to identify small molecules in an astronomical observation without the aid of high-resolution experimental data. We also report dipole moment values and show that the above-mentioned cyclic isotopologues have values of 0.094, 0.225, and 0.312 D, respectively, while the l-C{sub 3}H{sub 3}{sup +} isotopologues have values that range between 0.325 and 0.811 D. Thus, it is hoped that the highly accurate spectroscopic constants and data provided herein for the {sup 13}C and deuterium isotopologues of the cyclic and linear forms of C{sub 3}H{sub 3}{sup +} will enable their identification in astronomical observations from the Herschel Space Observatory, the Stratospheric Observatory for Infrared Astronomy, the Atacama Large Millimeter Array, and in the future, the James Webb Space Telescope.