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The submillimeter-wave spectrum of H2O2 has been recorded by means of a tunable FIR spectrometer. Stark measurements have been performed on three selected transitions in the n = 0 state, namely, the 2(20)-1(10) (tau = 4

High-resolution vibration-rotation spectra of 13 C 2 H 2 have been recorded in the wavenumber regions 1100-1240, 1730-1810, 2550-2700, and 3130-3280 cm −1 at Doppler- or pressure-limited resolution. In these spectral ranges bands involving the ν 1 and ν 2 stretchings and the bending-stretching combination levels with v 2 = 1, v 4 = 1, v 5 ≤ 2 have been analyzed. The main purpose of the analysis was the treatment of the Fermi resonance occurring between the ν 1 (Σ + g ) and the ν 2 + 2ν 5 (Σ + g ) levels, detected as ν 1 ← ν 5 and ν 2 + 2ν 5 ← ν 5 hot bands in the 4-μm region. The global analysis of all the observed transitions provided a set of 20 molecular parameters which fully characterize the stretching and bending-stretching combination states. The vibrational coupling terms which describe the Fermi resonance are also computed with high accuracy.

Vibration-rotation spectra of 13 C 2 H 2 and 12 C 13 CH 2 have been recorded in absorption in selected regions between 50 and 1450 cm −1 at resolutions varying from 0.002 to 0.006 cm −1 , with two different FT spectrometers. Many bands involving the bending modes ν 4 and ν 5 are present in this wavenumber range. Those with v 4 + v 5 = 2 have been analyzed by adopting a model Hamiltonian which accounts for the l -type resonances. All the relevant vibrational and rotational constants have been fitted for 13 C 2 H 2 whereas the anharmonic constant x 0 44 could not be determined for 12 C 13 CH 2 because of the lack of observation of transitions involving the 2ν 4 levels. The spectrum of 13 C 2 H 2 consisted of 1203 measured lines which required 38 molecular paramelers in order to obtain a good fit. The weaker spectrum of 12 C 13 CH 2 contained only 519 lines and 28 parameters were found to be sufficient.