title: Inelastic collisions in molecular nitrogen at low temperature (2 < or = T < or = 50 K).
abstract: Theory and experiment are combined in a novel approach aimed at establishing a set of two-body state-to-state rates for elementary processes ij --> lm in low temperature N(2):N(2) collisions involving the rotational states i,j,l,m. First, a set of 148 collision cross sections is calculated as a function of the collision energy at the converged close-coupled level via the MOLSCAT code, using a recent potential energy surface for N(2)-N(2). Then, the corresponding rates for the range of 2 < or = T < or = 50 K are derived from the cross sections. The link between theory and experiment, aimed at assessing the calculated rates, is a master equation which accounts for the time evolution of rotational populations in a reference volume of gas in terms of the collision rates. In the experiment, the evolution of rotational populations is measured by Raman spectroscopy in a tiny reference volume (approximately 2 x 10(-3) mm(3)) of N(2) traveling along the axis of a supersonic jet. The calculated collisional rates are assessed experimentally in the range of 4 < or = T < or = 35 K by means of the master equation, and then are scaled by averaging over a large set of experimental data. The scaled rates account accurately for the evolution of the rotational populations measured in a wide range of conditions. Accuracy of 10% is estimated for the main scaled rates.
authors.affiliation: Instituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain.
authors.forename: J P
authors.initials: JP
authors.lastname: Fonfría
authors.forename: A
authors.initials: A
authors.lastname: Ramos
authors.forename: F
authors.initials: F
authors.lastname: Thibault
authors.forename: G
authors.initials: G
authors.lastname: Tejeda
authors.forename: J M
authors.initials: JM
authors.lastname: Fernández
authors.forename: S
authors.initials: S
authors.lastname: Montero