Laser enhanced chemical reaction studies. Technical report, January 1, 1994--February 28, 1995

The relaxation of vibrationally excited pyrazine (E=40,640 cm{sup -1}) by collisions which populate the high J tail (J=58-82) of the vibrationless ground state (00{sup 0}0) of CO{sub 2} has been studied using tunable infrared diode lasers to probe the scattered CO{sub 2} molecules. The nascent rotational populations and translational recoil velocities for a series of rotational states in the high J tail of the 00{sup 0}0 level of CO{sub 2} were measured at five collision cell temperatures: 243, 263, 298, 339, and 364 K. Both the rate constants describing these V-R/T processes and the translational temperatures describing the recoiling CO{sub 2} molecules exhibit a very weak positive temperature dependence indicating that the high energy CO{sub 2} molecules must originate from near the center of the pre-collision energy distribution. Quantitative estimates of the actual amount of energy transferred in collisions between CO{sub 2} and vibrationally excited pyrazine, based on an angular momentum and translational energy exponential gap model of the cross section, indicate that {triangle}E{sub total} can be as large as 7090 cm{sup -1} ({approximately}20 kcal/mol). These experiments offer compelling evidence that these energy transfer events can indeed be classified as supercollisions since they involve unusually large, single collision energy transfer magnitudes; and despite their relative infrequency, they play a most important role in the collisional deactivation of vibrationally excited pyrazine by a CO{sub 2} bath