Kinetic Investigation of the Reaction Sr(¹S) + O₂ + He in the Temperature Range from 303 to 968 K

Abstract

A kinetic study of the third-order recombination reaction Sr( 1 S) + O 2 + He 98 k 1 (He) SrO 2 + He has been carried out in a fast-flow reactor in the temperature and pressure range of respectively 303-968 K and 6-12 Torr. Strontium atoms were generated by thermal evaporation of strontium metal pellets and then monitored by atomic absorption spectroscopy (AAS). The Arrhenius plot shows a departure from linearity above 500 K. The modified Arrhenius expression taking into account a temperature dependence of the preexponential factor for the entire temperature range results in the expression k 1 Sr (He) ) [(1.9 ( 0.3) × 10 -23 ]T -1.7 exp-[(-12.1 ( 0.8 kJ mol -1 )/RT] cm 6 molecule -2 s -1 . The best representation of the temperature dependence is given by the polynomial fit log k 1 Sr (He) = -60.83 + 22.44(log T) -3.89(log T) 2 . A lower limit to the bond energy of the SrO 2 ( 3 A 2 ) reaction product is estimated by means of the method based on the expression of the equilibrium constant and the theory of statistical mechanics. A value of D 0 > 244 kJ mol -1 was obtained, which is in the range of the values derived from ab initio calculations.

Effects of Plume Hydrodynamics and Oxidation on the Composition of a Condensing Laser-Induced Plasma

“…While molecular emission may be visible at 550 ns, these features are significantly more intense at later times. ZrO emission bands from the c 3 Π 2 −a 3 Δ 3 (0,0) ZrO transition 23 are clear in the 3050 and 5050 ns spectra, in the region highlighted in blue. The SrO orange band is evident as a broad, doublehumped feature at 5050 ns (shown highlighted in red) and is likely the convolution of the emission from multiple SrO transitions, including at least two identified 3 Π-3 Π transitions.…”

Kinetic Investigation of the Reactions of Mg(1S), Ca(1S), and Sr(1S) Atoms with NO2 over the Temperature Ranges 303−836, 303−916, and 303−986 K, Respectively

“…The experimental setup has been amply described in earlier publications, − and only a brief summary will be presented here. It consists of two major parts: a fast-flow reactor under low pressure and an AAS detection technique.…”

“…This study of the alkaline earth metal atom reactions with NO 2 forms part of a broader kinetic investigation of the reactions of these metals with several molecules such as O 2 , N 2 O, and Cl 2 . − The reason for selecting these compounds is that each of the reactions with these molecules proceeds according to a different reaction mechanism.…”

“…Indeed the alkaline earth metal atom reactions with oxygen are third-order reactions showing a positive temperature dependence due to an energy barrier at the intersection of the covalent and ionic potential energy surface of the reacting species. − ,, All of the very exothermic N 2 O reactions show a relatively high activation energy, associated with the closed-shell character of both reaction partners . The Cl 2 reactions are very fast and are explained in terms of the electron jump mechanism .…”

Transitions in Order and Molecularity with Temperature in Gaseous Metal Oxidation Reactions. The Sb-O2 System

“…Where abstraction is too endothermic, O 2 forms association or insertion complexes, e.g. with alkali metals, Mg, Ca, Sr [2,7,8], Fe [9], Cu [7,10], Cr and Ni [10]. However, in the limited temperature ranges of these studies no transition from ter-, to bi-molecular reaction was seen.…”