Theoretical modelling and experimental studies of the multi-quantum vibration exchange in vibrationally excited CO molecules

Abstract

Studies of the vibration-vibration (VV) exchange in CO molecules excited up to vibration quantum numbers v = 20 have been performed both theoretically and experimentally. A new kinetic model which takes into account the multi-quantum VV exchange in the temperature range T = 100-300 K is described for the first time. A description is given of the experimental methodology allowing for studies of the effects of the relaxation of the vibrational distribution after a sudden disturbance. The disturbance of the vibrational distribution is produced by a Q-switched short pulse of single line radiation in fundamental band. The relaxation is studied by measuring the laser pulse energy of the second pulse initiated by resonator Q-switching produced with a variable time delay relative to the first pulse. A set of kinetic rate constants accepted in the model for various gas temperatures, vibration level numbers and number of exchanged vibration quanta from 1 to 4 is presented. The good agreement between the experimental data and the results of the advanced theory is the first direct evidence in support of the multi-quantum exchange model.

Sensitivity of molecular vibrational dynamics to energy exchange rate constants

“…It is interesting that the two versions of the MQE model have similar v-dependence of VV exchange frequency. It has been previously shown [14] that model II describes high levels population dynamics in a more realistic way than model I. The same conclusion holds for model III.…”

“…Laser parameters, in particular when operated in a selective mode, are controlled by VV exchange processes within a local region of vibrational levels where the VDF is disturbed by laser action. It was shown in [14] that dynamics of local disturbances of the VDF can be characterized by a local frequency of VV exchange collisions, resulting in the removal of a CO molecule from the selected level, v. It can be expressed in the form…”

“…A key issue in whether the formulated model gives a good description of the CO overtone laser is the correct choice of a set of VV exchange rate coefficients. Historically, the first model of the CO overtone laser where the MQE processes were introduced [14] was based on earlier published results of semiclassical calculations of the EERCs [15,16]. Because of the incompleteness of published data a procedure of extrapolation of the EERC values for processes where numerical data were missing was developed in [14].…”

“…The first (I) is based on the SQE approximation. The second (II) is based on the MQE theory published in [14], using previously computed energy exchange rate constants (EERCs) [15,16]. The last MQE version (III) is based on the most recent corrected data on EERCs and is described in this paper.…”

Vibrational energy exchanges between N2and strongly excited CO molecules: their role in vibrational kinetics

“…The achievement of these new results encouraged the revision of CO laser kinetic modelling by incorporating the rate constants available at that time for the MQE processes in CO-CO collisions [10][11][12]. A better knowledge of the CO-CO intermolecular potential stimulated the calculations of a large set of updated V-V rate constants [18], and most recently, the complete version of the kinetic model of the CO laser for N 2 -free mixtures was recently published [6].…”