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Author(s):   Plane, J.M.C.; Rollason, R.J.
Title:   Kinetic Study of the Reactions of CaO with H2O, CO2, O2, and O3: Implications for Calcium Chemistry in the Mesosphere
Journal:   J. Phys. Chem. A
Volume:   105
Page(s):   7047 - 7056
Year:   2001
Reference type:   Journal article
Squib:   2001PLA/ROL7047-7056

Reaction:   CaO + O3CaO2 + O2
Reaction order:   2
Temperature:   204 - 318 K
Pressure:  3.73E-3 - 1.05E-2 bar
Rate expression:   5.7x10-10 [±1.7x10-10 cm3/molecule s] e-2220 [±620 J/mole]/RT
Bath gas:   N2
Category:  Experiment
Data type:   Absolute value measured directly
Pressure dependence:   None reported
Experimental procedure:   Static or low flow - Data taken vs time
Excitation technique:   Flash photolysis (laser or conventional)
Time resolution:   In real time
Analytical technique:   Laser induced fluorescence
Comments:   CaO was generated by 193 nm excimer laser photolysis of Ca(acac)2 calclium acetyl acetonate. The time decay of CaO was monitored by LIF pumping at 385.9 nm and detecting at >693 nm. O3 was monitored by absorption at 253.7 nm using a mercury lamp. Absolute uncertainties in rate constants were estimated at 22%. RRKM analysis was used to extrapolate to high and low pressure rate expressions. Reactions appeared to be slightly in fall-off, thus high pressure rate coefficients should be good, while low pressure rate parameters are less certain. Quantum DFT calculations B3LYP/6-311+G(2d,p) to calculated geometries, vibrational frequencies, and energies of reactants, products, and transition states and to determine reaction pathways.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) [cm3/molecule s]
204 1.54E-10
225 1.74E-10
250 1.96E-10
275 2.16E-10
300 2.34E-10
318 2.46E-10