The structure and electric dipole moment of camphor determined by rotational spectroscopy

Abstract

The rotational spectrum of camphor was investigated for the first time. Accurate spectroscopic constants for the parent isotopomer were determined from measurements in supersonic expansion at 6.7–18.5 GHz, and on a room-temperature sample at 173–222 GHz. All three types of allowed dipole moment transitions, μ_a, μ_b, μ_c, were observed. The supersonic expansion spectrum allowed measurement, in natural abundance, of all ten singly substituted ¹³C isotopomers, as well as of the ¹⁸O isotopomer. The rotational constants were used to determine the r_s, r₀, and the r⁽¹⁾_m gas-phase geometries of the camphor molecule. The electric dipole moment of camphor was determined from Stark effect measurements, and is |μ_a| = 2.9934(23) D, |μ_b| = 0.7298(6) D, |μ_c| = 0.0804(7) D, μ_tot = 3.0821(22) D. The experimental results are compared with predictions from ab initio calculations and with the geometry of solid camphor.