Towards an understanding of the helium–acetylene van der Waals complex

Abstract

The weakly bound complex He–C₂D₂ is studied in the ν ₃ fundamental band of C₂D₂ (≈2440 cm⁻¹) using a tuneable infrared diode laser to probe a pulsed supersonic slit jet expansion. This is the first published spectrum for helium–acetylene. Transitions observed in the region of the C₂D₂ R(0) line are assigned with the help of theoretical results based on an ab initio intermolecular potential, and fitted using a simple Coriolis model. The results indicate that the complex is rather close to the free rotor limit, helping to explain the absence of previous data. Scaled parameters from the model are used to predict a spectrum for He–C₂H₂.

Keywords:

• helium
• acetylene
• dimer
• spectroscopy
• infrared
• van der Waals

Acknowledgements

We thank L. Murdock for technical assistance and J. Norooz Oliaee for help with the experiment. We gratefully acknowledge the financial support of the Canadian Space Agency and the Natural Sciences and Engineering Research Council of Canada. This work has been supported by the Ministerio de Ciencia e Innovación, the Xunta de Galicia, and FEDER (CTQ2008-01861/BQU, CTQ2011-29311-C02-01, and INCITE09 314 252 PR projects).