Infrared spectra of acetylene dimers and acetylene-nitrogen: (DCCD) 2, H-bonded DCCD-HCCH, and DCCD-NN in the 4.1 μm region

Lauzin, Clément [UCL] Moazzen-Ahmadi, N. McKellar, A.R.W.

Infrared spectra of the weakly-bound T-shaped acetylene dimers DCCD-DCCD and DCCD-HCCH are studied in the region of the DCCD ν 3 fundamental (∼2440 cm -1) using a pulsed supersonic slit-jet expansion and a tunable diode laser probe. The K a = 0 ← 1 and 1 ← 0 subbands, corresponding to the vibration of the DCCD monomer at the "top" of the T, are analyzed. Compared to the analogous spectrum of HCCH-HCCH, the present results are much less perturbed. The tunneling splitting for (DCCD) 2 in the excited state is determined to be 141 MHz, a big reduction from the previously determined ground state value of 424 MHz. The dimer A rotational constants show a large apparent increase upon vibrational excitation, and we discuss whether this increase is real. The linear DCCD-NN complex is also observed as an impurity in the spectrum, and it too is found to be unperturbed, in contrast with HCCH-NN. © 2011 Elsevier Inc. All rights reserved.