Rotational spectrum of CNCN in excited vibrational states

Abstract

The millimeter-wave rotational spectrum of isocyanogen, CNCN, was measured in the frequency range from 70 to 340 GHz in the vibrational ground state and in the excited vibrational bending states ( v 4 v 5) = (00), (10), (01), (02), (03), (11). Accurate molecular constants were determined using the effective Hamiltonian for linear polyatomic molecules defined by K. M. T. Yamada, F. W. Birss, and M. R. Aliev [ J. Mol. Spectrosc. 112, 347–356 (1985)]. The rotational transitions J = 2 ← 1 and J = 3 ← 2 were measured in the microwave regions 20 690–20 970 and 29 940–30 420 MHz, respectively, in order to search for rotational transitions arising from molecules in the vibrational states ν 3 and 2 ν 4 coupled by a Fermi resonance predicted by P. Botschwina and P. Sebald [ Chem. Phys. 141, 311–323 (1990)]. This resonance could be found and confirmed from the pure rotational transitions. The spectroscopic constants B v and D v as well as several vibration-rotational constants for each vibrational state of CNCN were determined.