Collisional Energy Transfer

The birth of a star - The birth of a star, visible as jets* emanating from a dense cloud, revealed by ALMA observations of CO (Credit : ESO).

*a so-called Herbig-Haro object

Observatories such as the ALMA interferometer situated in the Chilean Andes represent an enormous investment in the area of molecular astronomy. Such molecules serve as sensitive physical and chemical probes of both the conditions and history/evolution of these exotic objects. Essential to the interpretation of such observations are data on how these small molecules exchange energy on collision with the majority species present in space, notably hydrogen and helium, in particular at the low temperatures prevailing in the dense molecular clouds where star formation begins. To date, observations of even simple species such as CO and especially hydrogen-containing molecules such as OH and CH depend entirely on calculated rates of collisional energy exchange. Such calculations are notoriously difficult to perform at the necessary level of accuracy, and so our aim here is to perform experimental measurements at the quantum state-to-state level of these energy exchange processes using a combination of pulsed infrared and ultraviolet laser probes within a unique ultracold hydrogen flow created within one of the CRESU (Reaction Kinetics in Uniform Supersonic Flow) apparatuses present within the IPR. This will enable quantitative comparisons with the latest theoretical calculations performed within the framework of the ANR project HYDRIDES (2013—2017).


  • [1] D. Carty, A. Goddard, I. R. Sims, and I. W. M. Smith, « Rotational energy transfer in collisions between CO(X-1 Sigma(+), v=2, J=0, 1, 4, and 6) and He at temperatures from 294 to 15 K, » J. Chem. Phys. 121 (10), 4671-4683 (2004).
  • [2] S. D. Le Picard, P. Honvault, B. Bussery-Honvault, A. Canosa, S. Laube, J. M. Launay, B. Rowe, D. Chastaing, and I. R. Sims, « Experimental and theoretical study of intramultiplet transitions in collisions of C(P-3) and Si(P-3) with He, » J. Chem. Phys. 117 (22), 10109-10120 (2002).
  • [3] S. D. Le Picard, B. Bussery-Honvault, C. Rebrion-Rowe, P. Honvault, A. Canosa, J. M. Launay, and B. R. Rowe, « Fine structure relaxation of aluminum by atomic argon between 30 and 300 K: An experimental and theoretical study, » J. Chem. Phys. 108 (24), 10319-10326 (1998).