| Abstrakt: |
The {}^{15}\hbox{N} fractionation in the thermal decomposition of nitrous oxide (\hbox{N}_2\hbox{O}) of natural isotopic composition has been'investigated in quartz reaction vessel in the temperature interval 888\ndash 1073\,\hbox{K} . The formulas relating the observed experimentally {}^{15}\hbox{N} fractionations with the primary {}^{15}\hbox{N} kinetic isotope effect, (k^{14}/k^{15})_{\rm p} for {}^{14}\hbox{N}{}^{15}\hbox{N}{}^{16}\hbox{O} , and secondary {}^{15}\hbox{N} kinetic isotope effect, (k^{14}/k^{15})_{\rm s} for {}^{15}\hbox{N}{}^{14}\hbox{N}{}^{16}\hbox{O} , have been derived. The experimentally estimated {}^{15}\hbox{N} kinetic isotope effects have been compared with the primary and secondary {}^{15}\hbox{N} kinetic isotope effects calculated with the absolute rate theory formulations applied to linear three atom molecules. A good agreement was found for the primary {}^{15}\hbox{N} kinetic isotope effect, (k^{14}/k^{15})_{\rm p} , in the temperature interval 888\ndash 1007\,\hbox{K} . But at 1073\,\hbox{K} the decompositions of \hbox{N}_2\hbox{O} , accompanied by NO (nitric oxide) formation proceed with a twice times smaller primary kinetic isotope effect, (k^{14}/k^{15})_{\rm p} of 1.0251 \pm 0.0009 , only, suggesting the nonlinear transition state structures with participation of the fourth external atom at high temperature decompositions of nitrous oxide. The nitrogen isotope effects determined in this study correlate well with nitrogen isotope fractionations observed in the natural biological, earth and atmospheric processes. [ABSTRACT FROM AUTHOR] |
