AB-INITIO ANHARMONIC-FORCE FIELDS AND SPECTROSCOPIC PROPERTIES FOR HC5N AND HC5NH+, MOLECULES OF INTEREST TO ASTROCHEMISTRY

Large-scale coupled cluster calculations have been carried out for HC5 N and HC5NH+. Accurate equilibrium geometries (ca. 0.0005 Angstrom acc uracy) are predicted for both species. The equilibrium rotational cons tant of HC5NH+ is B-e = 1294.1 MHz, which should also be a good estima te for the ground-state value B-0. HC5NH+ has a remarkably large equil ibrium dipole moment of mu(e) = 3.811 D and may thus by a suitable can didate for forthcoming investigation by microwave spectroscopy and rad io astronomy. For HC5N, strong anharmonic interaction is predicted bet ween mu(2) and 2 nu(5) as well as between nu(1), and nu(3) + nu(5). (C ) 1997 Elsevier Science B.V.