Mikrowellenspektrum, Hinderungspotential der internen Rotation, Quadrupolkopplungskonstanten und Dipolmoment des 2-Methyl-Pyridins

Abstract

Abstract The microwave rotational spectrum of 2-methyl-pyridine (a-picoline) has been investigated in the region from 6 to 30 kmc/s. From the three lowest states of internal rotation m=0, 1, 2 the three-and sixfold components V3 and V6 of the potential barrier hindering the internal rotation have been determined to be V3= (258,4 ± 0,1) cal/mole and V6=(-11,8± 0,1) cal/mole. From the splitting of low-J lines m=0 the nuclear quadrupole coupling constants for the 14N nucleus have been derived as χaa= (-0,33 ± 0,02) mc/s, χbb = (-2,86 ± 0,02) mc/s, χcc = (+3,19 ± 0,02) mc/s. The hyperfine structure of rotational transitions in excited states of internal rotation could also be accounted for with these coupling constants. The dipole moment components derived from Stark-effect measurements in the ground torsional state m = 0 are μa = (0,72 ± 0,01) Debye and μb - (1,71 ± 0,02) Debye.