Konstantinos S. Kalogerakis

Measurement of the rate coefficient for collisional removal of O{sub 2}(X {sup 3}{sigma}{sub g}{sup -},{upsilon}=1) by O({sup 3}P)

We report a laboratory measurement of the rate coefficient for the collisional removal of O{sub 2}(X{sup 3}{sigma}{sub g}{sup -},{upsilon}=1) by O({sup 3}P) atoms. In the experiments, 266-nm laser light photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O{sub 2}(a{sup 1}{delta}{sub g}) that is rapidly converted to O{sub 2}(X{sup 3}{sigma}{sub g}{sup -},{upsilon}=1-3) in a near-resonant electronic energy-transfer process with ground-state O{sub 2}. In parallel, a large amount of O({sup 1}D) atoms is generated that promptly relaxes to O({sup 3}P). Under the conditions of the experiments, only collisions with the photolytically produced O({sup 3}P) atoms control the lifetime of O{sub 2}(X{sup 3}{sigma}{sub g}{sup -},{upsilon}=1), because its removal by molecular oxygen at room temperature is extremely slow. Tunable 193-nm laser light monitors the temporal evolution of the O{sub 2}(X{sup 3}{sigma}{sub g}{sup -},{upsilon}=1) population by detection of laser-induced fluorescence near 360 nm. The removal rate coefficient for O{sub 2}(X{sup 3}{sigma}{sub g}{sup -},{upsilon}=1) by O({sup 3}P) atoms is (3.2{+-}1.0)x10{sup -12} cm{sup 3} s{sup -1} (2{sigma}) at a temperature of 315{+-}15 K (2{sigma}). This result is essential for the analysis and correct interpretation of the 6.3-{mu}m H{sub 2}O({nu}{sub 2}) band emission in the Earths mesosphere and indicates thatmorexa0» the deactivation of O{sub 2}(X {sup 3}{sigma}{sub g}{sup -},{upsilon}=1) by O({sup 3}P) atoms is significantly faster than the nominal values recently used in atmospheric models.«xa0lessWe report a laboratory measurement of the rate coefficient for the collisional removal of O2(XΣg−3,υ=1) by O(P3) atoms. In the experiments, 266-nm laser light photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O2(aΔg1) that is rapidly converted to O2(XΣg−3,υ=1–3) in a near-resonant electronic energy-transfer process with ground-state O2. In parallel, a large amount of O(D1) atoms is generated that promptly relaxes to O(P3). Under the conditions of the experiments, only collisions with the photolytically produced O(P3) atoms control the lifetime of O2(XΣg−3,υ=1), because its removal by molecular oxygen at room temperature is extremely slow. Tunable 193-nm laser light monitors the temporal evolution of the O2(XΣg−3,υ=1) population by detection of laser-induced fluorescence near 360 nm. The removal rate coefficient for O2(XΣg−3,υ=1) by O(P3) atoms is (3.2±1.0)×10−12cm3s−1(2σ) at a temperature of 315±15K(2σ). This result is essential for the a...

Product rotational distributions and specific opacity functions for the reaction Ba +HI → BaI (v=0,4,8,12,16,18) +H

The reaction Ba+HI→BaI(v)+H was studied under beam‐gas, single‐collision conditions with an average center‐of‐mass collision energy of 13 kJ mol−1. BaI (v) rotational distributions were recorded for v=0, 4, 8, 12, 16, and 18 by means of selectively detected laser‐induced fluorescence of the BaI Cu20092Π–Xu20092Σ+ band system. Each rotational distribution exhibits a maximum toward its high energy end and the range of rotational states becomes narrower as product vibration increases. Because the kinematic constraint causes almost all reagent orbital angular momentum to appear in product rotation, the principle of angular momentum conservation provides the means for determining specific opacity functions from the rotational distributions and the reagent relative velocity distribution. The specific opacity functions are narrow functions of the impact parameter. The peak values decrease smoothly from approximately 4.5 A for v=0 to 1.5 A for v=18, indicating a strong correlation between impact parameter and product vib...

Energy and angular momentum control of the specific opacity functions in the Ba+HI→BaI+H reaction

Crossed‐beam and beam‐gas experiments on the reaction Ba+HI→BaI+H have been performed, in which the most probable collision energy ranges from 3 to 17 kcal/mol. The results, combined with previous experimental studies on this reaction system, show a remarkable collision energy dependence. Between low and high collision energies, a transition occurs in the intensity, width, and peak location of the product vibrational and rotational population distributions. The onset of this transition is estimated to occur at approximately 5 kcal/mol. For collision energies smaller than 5 kcal/mol, the product vibrational distribution is bell shaped and peaks at v=12. For collision energies larger than 5 kcal/mol, a second maximum appears at v=0 in the vibrational distribution. The rotational distributions of the crossed‐beam experiments are extremely narrow but broaden at lower collision energies. As the collision energy is increased above 5 kcal/mol, the BaI rotational excitation is very near the energetic limit, and t...