ROVIBRATIONAL SPECTROSCOPY OF (CCL4)-CL-35

High-resolution rotationally resolved infrared spectra of the spherica l-top rotor (CCl4)-Cl-35 (in samples of natural isotopic composition) were obtained both in static cells by FTIR spectroscopy (nu(4), upsilo n(1) + nu(4)) and in a supersonically cooled expansion with tunable di ode lasers (nu(3)). For the nu(3) fundamental at 799 cm(-1), quantum a ssignments were made for individual transitions from P(20) to R(24), a nd the partially resolved Q branch was matched with synthesized spectr a. The bands nu(4) (316 cm(-1)) and nu(1) + nu(4) (774 cm(-1)) exhibit much reduced manifold splitting, and scalar fits were made to the R(2 4)-R(70) and P(38)-R(56) frequencies, respectively. The nu(3)/(nu lamb da(1) + nu(4)) Fermi dyad yields Coriolis constants zeta(3) = 0.621 an d zeta(4) = -0.145 that satisfy the harmonic sum rule, but are perturb ed by the Fermi resonance and are inconsistent with intramolecular for ce fields previously reported based on isotope shifts in matrix spectr a. The true bending-mode Coriolis constant zeta(4) = -0.414, obtained from analysis of the isolated and unperturbed nu(4) band, agrees well with the isotope shifts. CCl4 and other tetrahedral XY(4) molecules ar e shown to vibrate according to a simple vector-displacement normal-mo de model for which zeta(3) approximate to 4/[3(m(x)/m(y)) + 4]. (C) 19 95 Academic Press, Inc.