Laboratory Study of O2(b1Σ g+, υ = 1) Collisional Removal at Thermospheric Temperatures

Details Laboratory Study of O2(b1Σ g+, υ = 1) Collisional Removal at Thermospheric Temperatures Laboratory Study of O2(b1Σ g+, υ = 1) Collisional Removal at Thermospheric Temperatures

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa12a1074w&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SA12A-1074

Physics

0300 Atmospheric Composition And Structure, 0310 Airglow And Aurora, 0394 Instruments And Techniques, 0399 General Or Miscellaneous

Scientific paper

In the Earth's thermosphere, energy transfer from O(1D) to O2 generates oxygen molecules in the υ = 0 and 1 levels of the O2(b1Σg+) state. The emissions in the O2(b1Σ g+ - X3Σ g-) system (Atmospheric Band) present a major component of the Earth's airglow. Interpretation of the measured intensities of O2 Atmospheric Band emissions can yield altitude profiles of oxygen atom density and local temperature in the lower thermosphere. To achieve this goal accurate laboratory measurements of the collisional removal rate coefficients of O2(b, υ = 1) and their temperature dependence are essential. Atmospheric observations suggest that the relevant colliders for the removal of O2(b, υ = 1) in the lower thermosphere are O2 and O(3P). We report measurements of the rate coefficients for the collisional removal of O2(b, υ = 1) by O2, N2, and CO2, at temperatures in the range 300--1000 K. A state-specific two-laser technique is used, in which the visible output of the first laser directly excites O2 to O2(b, υ = 1), and the ultraviolet output of the second laser probes the O2(b, υ = 1) population by resonantly enhanced multiphoton ionization via the υ= 4 level of the d1Π g Rydberg state. The temporal evolution of the O2(b, υ = 1) population is monitored by varying the time delay between the two laser pulses. The rate coefficient of the collisional removal of O2(b, υ = 1) by O2 increases monotonically with temperature from about 1.5 x 10-11 cm3 s-1 to about 6*E-11 cm3 s-1 in the range 300--1000 K. Experiments with colliders N2 and CO2 determine the upper limits for the removal rate coefficients of O2(b, υ = 1) by N2 and CO2 to be 2 orders of magnitude smaller. This work extends previous studies of O2(b, υ = 1) at room and low temperatures.1,2 We are currently planning experiments to investigate the collisional removal of O2(b, υ = 1) by O atoms.
This study was supported by the NSF's Grant ATM-0209229. The participation of K. Phillips in this project was funded by NSF's Research Experiences for Undergraduates (REU) Program (Grant PHY-0097861). We wish to thank Drs. Richard A. Copeland and Tom G. Slanger for many insightful comments and discussions.
1. H. I. Bloemink, R. A. Copeland, and T. G. Slanger, J. Chem. Phys. 109, 4237 (1998).
2. E. S. Hwang, A. Bergman, R. A. Copeland, and T. G. Slanger, J. Chem. Phys. 110, 18 (1999).

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