The gas-phase IR spectrum of the n2 ( A1, 1610.33 cm21) band of the deuterated isotopomer of diazirine, D2CN2, a
three-membered ring compound which belongs to the molecular symmetry point group C2v, has been studied at a resolution
of about 0.005 cm21. This vibrational mode which can be approximately described as NAN stretching is widely perturbed.
This is due to various interactions with the tetrad consisting of the binary combinations n 6 1 n 7 ( A1), n 7 1 n 9 ( A2), n 5 1
n 6 (B2), and n 5 1 n 9 (B1), which form a relatively isolated pentad together with n2 in the wavenumber region 1560–1610
cm21. A simultaneous upper state analysis of n2 from a pentad model including these resonances has been performed and a
set of spectroscopic parameters has been obtained. Since the four combination bands of the pentad are dark states, only band
centers could be determined; in addition for n5 1 n9 and n7 1 n9 also the term (B 2 C)/ 2 has been obtained. A number of
Coriolis interaction constants and the vibrational resonance (with n6 1 n7) parameter have been calculated as well.
