Kinetic Study of Ca(1S) + N2O and Sr(1S) + N2O Reactions in the Temperature Ranges of, Respectively, 303−1015 and 303−999 K

A kinetic study of the second-order reactions Ca( 1 S) + N 2 O(X 1 Σ + ) CaO + N 2 and Sr( 1 S) + N 2 O(X 1 Σ + ) SrO + N 2 has been carried out in a fast-flow reactor in the temperature ranges of, respectively, 303−1015 and 303−999 K. The alkaline earth metal atoms were thermally generated from the solid metal pellets. Their decays as a function of the added N 2 O concentration were followed by means of atomic absorption spectroscopy (AAS) at 422.7 nm for calcium and 460.7 nm for strontium atoms. Both reactions showed a non-Arrhenius behavior that can best be explained by the presence of two reaction product channels, resulting in a rate constant expressed as the sum of two exponential functions: k 1 Ca = [(1.9 ± 1.4) × 10 -8 ] exp[(−40.6 ± 4.7 kJ mol -1 )/( RT )] + [(2.8 ± 0.7) × 10 -10 ] exp[(−14.1 ± 0.7 kJ mol -1 )/( RT )] cm 3 molecule -1 s -1; k 1 Sr = [(1.1 ± 0.2) × 10 -9 ] exp[(−23.3 ± 1.3 kJ mol -1 )/( RT )] + [(1.1 ± 0.1) × 10 -10 ] exp[(−8.8 ± 0.4 kJ mol -1 )/( RT )] cm 3 molecule -1 s -1 . The best fits over the entire temperature range are given by the polynomial expressions log k 1 Ca = −30.12 + 9.78(log T ) − 0.99(log T ) 2 and log k 1 Sr = −26.02 + 8.40(log T ) − 1.02(log T ) 2 . The results will be discussed in view of the literature data on the alkaline earth metal atom + N 2 O reactions. The experimentally derived energy barriers will be compared with the calculated values on the basis of the semiempirical configuration interaction theory (SECI). Reasonable good correlations were obtained between the barrier heights of the reaction and the promotion energy of the metals involved.