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Author(s):   Rollason, R.J.; Plane, J.M.C.
Title:   A Kinetic Study of the Reactions of MgO with H2O, CO2 and O2: Implications for Magnesium Chemistry in the Mesosphere
Journal:   Phys. Chem. Chem. Phys.
Volume:   3
Page(s):   4733 - 4740
Year:   2001
Reference type:   Journal article
Squib:   2001ROL/PLA4733-4740

Reaction:   CO2 + MgOMgCO3
Reaction order:   3
Temperature:   202 - 371 K
Pressure:  3.87E-3 - 4.16E-2 bar
Rate expression:   1.19x10-28 [cm6/molecule2 s] (T/298 K)-2.76 e-2928 [J/mole]/RT
Uncertainty:   1.3
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:   Paper gives low pressure rate expression as log(ko) = -33.7 + 5.827*log(T) ?.494*(log(T))2using fitted Lindemann expression with Fc=0.37Abstractor fit low pressure rate expression to extended Arrhenius form.

MgO was generated by 193 nm excimer laser photolysis of Mg(acac)2 magnesium acetyl acetonate in the presence of O3. The time decay of MgO was monitored by LIF pumping at 499.4 nm and detecting at >600 nm. O3 was monitored by absorption at 253.7 nm using a mercury lamp. Absolute uncertainties in rate constants were estimated at 30%. RRKM analysis was used to extrapolate to high and low pressure rate expressions. Reactions appeared to be only very 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]
202 6.09E-29
225 5.41E-29
250 4.73E-29
275 4.13E-29
300 3.61E-29
325 3.17E-29
350 2.79E-29
371 2.52E-29