Microwave spectrum, dipole moment, quadrupole coupling constants, and conformation of cyanocyclobutane

Abstract

The microwave spectrum of cyanocyclobutane has been observed in the ground and first four excited vibrational states. The spectrum consisted of a‐ and c‐type R‐ and Q‐branch transitions. 14 Nquadrupole coupling constants were determined to be χ aa = −3.663± 0.005 MHz , χ bb = 2.086± 0.006 MHz and χ cc = 1.577± 0.006 MHz . Electric dipole momentmeasurements led to μ a = 4.00 ± 0.003 D and μ c = 0.95± 0.02 D (μ b = 0 by symmetry). All of the data are in accord in specifying the equatorial conformation for the puckered‐ring system. Data from the excited states of the ring‐puckering motion are in accord with a recently proposed potential function.