Rotational spectra of quinoline and of isoquinoline: spectroscopic constants and electric dipole moments

Abstract

Rotational spectra of quinoline and of isoquinoline have been observed in the centimeter- and millimeter-wave regions. The spectra were assigned on the basis of bands formed by high- J transitions, which were measured up to J″⩽128 and ν⩽234 GHz. Complementary measurements were also made on low- J, centimeter-wave spectra observed in supersonic expansion and with fully resolved nuclear quadrupole hyperfine structure. Accurate rotational, centrifugal distortion and hyperfine splitting constants for the ground states of both molecules are reported. The electric dipole moments for the two molecules were also determined from Stark effect measurements and are μ a =0.14355(19), μ b =2.0146(17), μ tot=2.0197(17) D for quinoline, and μ a =2.3602(21), μ b =0.9051(14), μ tot=2.5278(20) D for isoquinoline. The experimental observables were found to be rather accurately predicted by MP2/6-31G** ab initio calculations, and corresponding molecular geometries are also reported.