Translationally and rotationally resolved excitation of CO2(002) by collisions with hot hydrogen atoms

Abstract

Articles you may be interested inCollisional excitation of CO2(0111) by hot hydrogen atoms: Alternating intensities in stateresolved vibrational, rotational, and translational energy transfer J. Chem. Phys. 93, 445 (1990); 10.1063/1.459718 Stateresolved vibrational, rotational, and translational energy deposition in CO2(0001) excited by collisions with hot hydrogen atoms J. Chem. Phys. 92, 4876 (1990); 10.1063/1.457704 Rotationally resolved hot atom collisional excitation of CO2 0001 and 0002 stretching vibrations by time resolved diode laser spectroscopy J. Chem. Phys. 88, 6240 (1988); 10.1063/1.454463Rotationally resolved isotope effect in the hot atom collisional excitation of CO2 (0001) by timedependent diode laser spectroscopy Rotationally resolved hot atom collisional excitation of CO2(0001) by timeresolved diode laser spectroscopy Time domain tunable diode laser absorption spectroscopy has been used to measure rotationally resolved transient absorption line shapes and nascent rotational populations for CO 2 molecules excited into the (00°2) vibrational state by collisions with translation ally hot hydrogen atoms. The 00°2 rotational population distribution and rotationally resolved linewidths are remarkably similar to those previously obtained for 00°1. Within the context of a simple physical model used to interpret the data, the similar rotational distributions and translational recoils for 00°1 and 00°2 suggest that these two states are excited by similar collision trajectories, wherein asymmetric stretching excitation is optimized when H strikes near the end of the O-C-O molecule. The magnitude of population scattered into 00°2 is -21 times smaller than that scattered into 00°1.

Vibrational Energy Transfer

“…The hot excited C 6 F 6 donor can be readily produced via absorption of a 248 nm excimer laser pulse followed by rapid internal conversion of electronic energy to vibrational energy. − The idea of the experiments is to “view” the collision through the eyes of the vibrationally excited bath molecule, CO 2 (00 0 1; J , V ), emerging from the collision. ,, The excited bath molecule can be probed using a high-resolution infrared laser that uniquely identifies the vibrational and rotational quantum numbers 00 0 1; J of the scattered CO 2 . Even the velocity of the bath molecule can be sensed by using this same infrared laser to measure the Doppler profile of the recoiling CO 2 (00 0 1; J , V ) at short times after the collision. ,,− Figure compares the laser line width to the Doppler profile of a thermal (300 K) CO 2 absorption and the Doppler profile of a typical recoiling molecule. The laser line width is 10 times narrower than even the room temperature spectroscopic absorption profile.…”

“…Even here the coupling of translational velocity recoil and angular momentum, predicted by conservation of orbital angular momentum in the collision process, ( h /2π)(Δ J ) = μ〈 V rel 〉 b , where h is Planck's constant, μ is the collision reduced mass, V rel is the collision recoil velocity in the center-of-mass frame, and b is the mean impact parameter, has been found to hold at least for the pyrazine/CO 2 collision system. , This suggests that the detailed partitioning of energy between rotational and translational degrees of freedom may be controlled by relatively simple kinematic factors. Nevertheless, the fact that the relationship between the recoil velocity and the change in angular momentum is related through the impact parameter should not be missed, since this is a flag that molecular orientation, point of impact, and distance of closest approach will control the fractional amount of energy transferred, respectively, to the rotational and translational degrees of freedom. − Ultimately, the hope lives that the intimate coupling among Δ J , V rel , and b can be unraveled, thus providing probes of the potential energy surface for the collision process.…”

“…Even the velocity of the bath molecule can be sensed by using this same infrared laser to measure the Doppler profile of the recoiling CO 2 (00 0 1;J,V) at short times after the collision. 93,94,[118][119][120][121][122][123] Figure 1 compares the laser line width to the Doppler profile of a thermal (300 K) CO 2 absorption and the Doppler profile of a typical recoiling molecule. The laser line width is 10 times narrower than even the room temperature spectroscopic absorption profile.…”

“…Nevertheless, the fact that the relationship between the recoil velocity and the change in angular momentum is related through the impact parameter should not be missed, since this is a flag that molecular orientation, point of impact, and distance of closest approach will control the fractional amount of energy transferred, respectively, to the rotational and translational degrees of freedom. [118][119][120][121][122][123] Ultimately, the hope lives that the intimate coupling among ∆J, V rel , and b can be unraveled, thus providing probes of the potential energy surface for the collision process.…”