ROTATIONALLY AND TRANSLATIONALLY RESOLVED HOT ATOM COLLISIONAL EXCITATION OF THE CO2 FERMI MIXED BEND STRETCH VIBRATIONAL LEVELS BY TIME-DEPENDENT DIODE-LASER SPECTROSCOPY

High resolution IR diode laser absorption spectroscopy is employed to monitor the nascent rotational population distributions and transient linewidths in the Fermi mixed symmetric stretch/overtone bend vibrationaJ mode of CO 2 (10°0/02°0) following collisions with translationally hot hydrogen and deuterium atoms, produced from the 193 nm excimer laser photolysis of H2S or D2S. The nascent 10°0/02°0 rotational distribution produced by H* atom collisional excitation peaks at J∼26 and is well fit by a 747 K Boltzmann distribution. The transient linewidths are 1.5-3 times the ambient, room temperature CO2 Doppler linewidths, are ∼0.002 cm-1 larger for D* atom collisions than H* atom collisions, and increase with increasing rotational quantum number. The experimentally determined relative cross sections for H* atom collisional excitation of CO2 vibrational states are as follows: 00°1 antisymmetric stretch: 10°0 Fermi mixed upper level: 02°0 Fermi mixed lower level: 0220 bend ≈ 1.0:0.6:0.6:0.4. The absolute cross section for inelastic collisional scattering of CO2 by H* atoms into 10°0 J=38 is (1.4±0.8)×10-2 Å2, and the total excitation cross section for the 10°0 vibrational state is 0.37±0.21 Å2. A statistical model and a simple quantized Landau-Teller model are unable to explain qualitatively the observed data; however, a breathing ellipsoid model, coupled with an IOS quantum scaling relation, reproduces the major features in the experimental data for both the 10°0/02°0 and 00°1 states. The differences in the experimental data for distinct vibrational motions can be attributed to hot atoms sampling different regions of the potential surface. © 1990 American Institute of Physics.