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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:   CO2 + CaOCaCO3
Reaction order:   3
Temperature:   213 - 480 K
Pressure:  3.73E-3 - 1.55E-2 bar
Rate expression:   1.56x10-26 [cm6/molecule2 s] (T/298 K)-3.64 e-4979 [J/mole]/RT
Bath gas:   N2
Category:  Experiment
Data type:   RRK(M) extrapolation
Pressure dependence:   Rate constant is low pressure limit
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:   Reported rate expression is log(ko) = -36.14 + 9.24*log(T) - 2.19* (log(T))^2. Authors used Lindemann expression with fitted Fc =0.36. Abstractor fit low pressure rate expression to extended Arrhenius form.

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) [cm6/molecule2 s]
213 3.18E-27
225 3.03E-27
250 2.69E-27
275 2.36E-27
300 2.07E-27
325 1.80E-27
350 1.57E-27
375 1.37E-27
400 1.19E-27
425 1.05E-27
450 9.18E-28
475 8.09E-28
480 7.89E-28