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Author(s):   Campbell, M.L.; Plane, J.M.C.
Title:   Kinetic Study of the Gas-Phase Reaction of Ca(1S0) with O2 from 296 to 623 K
Journal:   J. Phys. Chem. A
Volume:   105
Page(s):   3515 - 3520
Year:   2001
Reference type:   Journal article
Squib:   2001CAM/PLA3515-3520

Reaction:   Ca + O2CaO2
Reaction order:   3
Temperature:   296 - 623 K
Pressure:  3.33E-3 - 0.13 bar
Rate expression:   4.36x10-28 [cm6/molecule2 s] (T/298 K)-1.31 e-10701 [J/mole]/RT
Uncertainty:   1.29999995
Category:  Experiment
Data type:   Absolute value measured directly
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:   Ca(1So) is ground state of calcium. Used 248 nm excimer laser photolysis of Ca(FOD)2 to produced Ca atoms. LIF excite at 422.67 nm and detect at 420 nm was used to detected Ca atoms. Measured the time dependent decay. Temperature 296-623 K. Bath gas N2 2.5-10 torr and reaction gas O2 50-1000 mtorr. At 296 K went upto 100 torr and still was significantly in fall off. Rate constants were analyzed using RRKM theory with best fit parameters Einf=8.47 kJ/mol, Rho=4.55 Angstroms, Eta/k=450 K, Alpha=1.74 and step down DeltaEdown=350 cm-1 and could be reproduced to 4-12%. Rate constants were fit to the Lindemann expression using a broadening factor Fc=0.67. Reported fitted high pressure rate expression kinf = 1.36E-10 exp(-1020/T) cm3/(molecule*s) and low pressure rate expression log(ko) = -57.10 + 19.70 log(T) ?3.410 (log(T))^2. Abstractor converted this low pressure rate expression by fitting to an extended Arrhenius form. A = 7.60E-25 n = 1.31 Ea = 1287 K. Authors did B3LYP/6-311+G(d,p) calculations and determined that the reaction may proceed on the triplet surface.

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Rate constant values calculated from the Arrhenius expression:

T (K)k(T) [cm6/molecule2 s]
296 5.69E-30
300 5.92E-30
325 7.42E-30
350 8.94E-30
375 1.04E-29
400 1.19E-29
425 1.33E-29
450 1.46E-29
475 1.58E-29
500 1.69E-29
525 1.79E-29
550 1.88E-29
575 1.97E-29
600 2.04E-29
623 2.10E-29