Inelastic Collisions of O₂ with He at Low Temperatures

Abstract

Rotationally inelastic collisions of O 2 with He in the 10-34 K thermal range are investigated by means of an experimental procedure based on supersonic gas jets probed by Raman spectroscopy. The procedure employs a kinetic master equation (MEQ) that describes the time evolution of the rotational populations of O 2 along supersonic jets of O 2 and He mixtures. The MEQ is expressed in terms of experimental quantities (number density and rotational populations) measured here, and state-to-state rate coefficients for the O 2 :He inelastic collisions calculated here, plus those for O 2 :O 2 collisions from the literature. An agreement with the experiments is accomplished for temperatures between 10 and 34 K. Within this thermal range, the role of the fine structure due to electron spin in the collision dynamics of O 2 is discussed.

Review of Optical Thermometry Techniques for Flows at the Microscale towards Their Applicability to Gas Microflows

“…To the best of our knowledge, Raman thermometry has not yet been applied to gas flows in microfluidic devices. So far it has been successfully applied to free (i.e., unconfined) flows such as miniflames [149] or supersonic gas microjets of H 2 , N 2 , O 2 , CO 2 , H 2 O (gas) and some of their mixtures [150][151][152][153][154]. In N 2 [155], O 2 [156], and CO 2 [157,158] the temperature was determined through the rotational populations from the rotational Raman spectra, while in H 2 the rotational populations were measured from the rotationallyresolved vibrational Q-branch [159,160].…”