ROTATIONAL AND ROVIBRATIONAL SPECTRUM OF (CNCN)-N-15-N-15 IN THE REGION OF THE BENDING MODES V(4),V(5), THE COMBINATION BAND V(4)+V(5) AND THE FERMI INTERACTING MODES V(3), 2V(4)

The high-resolution gas-phase Fourier transform infrared spectrum of t he doubly N-15-substituted isocyanogen, (CNCN)-N-15-N-15, has been mea sured in the spectral regions 160-240 cm(-1) and 390-1110 cm(-1) with unapodized resolutions of 0.0017 and 0.0021 cm(-1) respectively. In th ese experiments we were able to measure the band systems due to the ex citation of the bending modes nu(5) and nu(4) at 190.9 cm(-1) and 458. 1 cm(-1), a combination band system of the two bending modes nu(4) + n u(5) at 649.7 cm(-1), as well as two band systems arising from a Fermi interaction between the twofold excited bending mode 2 nu(4) and the stretching mode nu(3) at 869.9 cm(-1) and 960.2 cm(-1) respectively. F urthermore, we have measured and assigned pure rotational transitions of (CNCN)-N-15-N-15 in the vibrational ground state and in excited vib rational bending states lying in the microwave and the millimeter wave region between 19.9 and 20.2 GHz, 29.9 and 30.4 GHz and 120 and 440 G Hz. Constants of a power series in J(J + 1) for numerous rovibrational subbands, as well as accurate molecular constants using the effective hamiltonian for linear polyatomic molecules, defined by Yamada et al. [J. Mel. Spectrosc, 112 (1985) 347], were determined.