Dariusz Golebiowski

Experimental 2CH excitation in acetylene-containing van der Waals complexes

Spectroscopic results are presented concerning the 2CH excitation around 1.5 µm in van der Waals complexes of acetylene (C2H2) with Ar, Kr, N2, CO2, N2O and C2H2. Many are reviewed from the literature, with some updates. Previously unpublished results are also presented, concerning the mechanism of formation of C2H2–Ar in the supersonic jet, the assignment of new spectral structures in C2H2–N2O, and the first observation of 2CH excitation in C2H2–Ne, C2H2–H2O, C2H2–D2O and (C2H2) n . Lifetimes of these 2CH vibrationally excited dimers are discussed.

Low-temperature high-resolution absorption spectrum of 14NH3 in the ν1+ν3 band region (1.51 μm)

Jet-cooled spectra of 14NH3 and 15NH3 in natural abundance were recorded using cavity ring-down (CRDS, 6584–6670 cm−1) and cavity enhanced absorption (CEAS, 6530–6700 cm−1) spectroscopy. Line broadening effects in the CRDS spectrum allowed lines with J″-values between 0 and 3 to be identified. Intensity ratios in 14NH3 between the jet-cooled CRDS and literature room-temperature data from Sung et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1066) further assisted the line assignments. Ground state combination differences were extensively used to support the assignments, providing reliable values for J, K and inversion symmetry of the ground state vibrational levels. CEAS data helped in this respect for the lowest J lines, some of which are saturated in the CRDS spectrum. Further information on a/s doublets arose from the observed spectral structures. Thirty-two transitions of 14NH3 were assigned in this way and a limited but significant number (19) of changes in the assignments results, compared to Sung et al. or to Cacciani et al. (J. Quant. Spectrosc. Radiat. Transfer, 113 (2012), 1084). Sixteen known and 25 new low-J transitions were identified for 15NH3 in the CRDS spectrum but the much scarcer literature information did not allow for any more refined assignment. The present line position measurements improve on literature values published for 15NH3 and on some line positions for 14NH3.

Femto-Fourier transform-cavity enhanced absorption spectroscopy in a supersonic expansion

Proofs of principle spectra of C2H4, N2O and C2H2, including H12C13CH in natural abundance, are reported, recorded in the 1.6 µm range in an Ar supersonic expansion using femto-Fourier transform–cavity enhanced absorption spectroscopy. The effective absorption pathlength in the jet-cooled sample is up to 78 m and the optimal S/N is over 2300. The data processing is detailed. Saturation effects are reported for the C2H2 bands.

Complementary cavity-enhanced spectrometers to investigate the OH + CH combination band in trans-formic acid

We have used continuous-wave cavity ring-down and femto-Fourier transform-cavity-enhanced absorption spectrometers to record the spectrum of the OH-stretching + CH-stretching (ν1 + ν2) combination band in trans-formic acid, with origin close to 6507 cm(-1). They, respectively, allowed resolving and simplifying the rotational structure of the band near its origin under jet-cooled conditions (Trot = 10 K) and highlighting the overview of the band under room temperature conditions. The stronger B-type and weaker A-type subbands close to the band origin could be assigned, as well as the main B-type Q branches. The high-resolution analysis was hindered by numerous, severe perturbations. Rotational constants are reported with, however, limited physical meaning. The ν1 + ν2 transition moment is estimated from relative intensities to be 24° away from the principal b-axis of inertia.