Rovibrational Spectroscopy of C 35Cl 4

Abstract

High-resolution rotationally resolved infrared spectra of the spherical-top rotor C 35Cl 4 (in samples of natural isotopic composition) were obtained both in static cells by FTIR spectroscopy (ν 4, ν 1 + ν 4) and in a supersonically cooled expansion with tunable diode lasers (ν 3). For the ν 3 fundamental at 799 cm −1, quantum assignments were made for individual transitions from P(20) to R(24), and the partially resolved Q branch was matched with synthesized spectra. The bands ν 4 (316 cm −1) and ν 1 + ν 4 (774 cm −1) exhibit much reduced manifold splitting, and scalar fits were made to the R(24)- R(70) and P(38)- R(56) frequencies, respectively. The ν 3/(ν 1 + ν 4) Fermi dyad yields Coriolis constants ζ 3 = 0.621 and ζ′ 4 = −0.145 that satisfy the harmonic sum rule, but are perturbed by the Fermi resonance and are inconsistent with intramolecular force fields previously reported based on isotope shifts in matrix spectra. The true bending-mode Coriolis constant ζ 4 = −0.414, obtained from analysis of the isolated and unperturbed ν 4 band, agrees well with the isotope shifts. CCl 4 and other tetrahedral XY 4 molecules are shown to vibrate according to a simple vector-displacement normal-mode model for which ζ 3 ≈ 4/[3( m x / m y ) + 4].