The high-resolution Fourier transform infrared spectrum of isocyanogen, CNCN: rovibrational analysis of the ν1 and ν2 stretching band systems

Abstract

The high-resolution gas phase Fourier transform infrared spectrum of the linear molecule isocyanogen, CNCN, has been measured in the 2000–2400 cm−1 region. The C≡N stretching band systems ν1 and ν2 located around 2302.0 and 2059.7 cm−1, respectively, were observed with an unapodized resolution of 0.003 cm−1. In the analysis of these band systems hot bands originating from the states with up to 3 quanta of ν5, the singly excited ν4, and the combination state (ν4 ν5) = (11) were assigned. Effective spectroscopic constants of the numerous subbands as well as constants of an effective Hamiltonian are presented. An analysis of rotation–vibration interaction in CNCN as well as a complete valence force field are presented. The equilibrium rotational constant Be of CNCN was found to be 5172.66 (18) MHz, the diagonal valence force constants determined for C=N–C≡N are for the Σ modes (in aJ/Å2): fC=N− = 15.1, f=N−C≡ = 8.3, f−C=N = 17.1, and for the Π modes (in aJ): fC=N−C≡ = 0.141, f=N−C≡N = 0.361.