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Titolo:
Studies of the thermal and photochemical decomposition mechanisms of (Bu2Se)-Se-t in the presence or absence of Me2Zn using deuterium labelled analogues
Autore:
Pickett, NL; Foster, DF; Maung, N; Cole-Hamilton, DJ;
Indirizzi:
Univ St Andrews, Sch Chem, St Andrews KY16 9ST, Fife, Scotland Univ St Andrews St Andrews Fife Scotland KY16 9ST Y16 9ST, Fife, Scotland NE Wales Inst, Adv Mat Res Labs, Wrexham LL11 2AW, Wales NE Wales Inst Wrexham Wales LL11 2AW t Res Labs, Wrexham LL11 2AW, Wales
Titolo Testata:
JOURNAL OF MATERIALS CHEMISTRY
fascicolo: 12, volume: 9, anno: 1999,
pagine: 3005 - 3014
SICI:
0959-9428(1999)9:12<3005:SOTTAP>2.0.ZU;2-D
Fonte:
ISI
Lingua:
ENG
Soggetto:
VAPOR-PHASE EPITAXY; BOND-DISSOCIATION ENERGIES; FREE-RADICAL MECHANISM; SHOCK TUBE TECHNIQUE; KINETIC DATA-BASE; COMBUSTION CHEMISTRY; CONTAINING MOLECULES; TEMPERATURE-RANGE; RATE CONSTANTS; MOVPE GROWTH;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Engineering, Computing & Technology
Citazioni:
71
Recensione:
Indirizzi per estratti:
Indirizzo: Cole-Hamilton, DJ Univ St Andrews, Sch Chem, St Andrews KY16 9ST, Fife, Scotland Univ St Andrews St Andrews Fife Scotland KY16 9ST tland
Citazione:
N.L. Pickett et al., "Studies of the thermal and photochemical decomposition mechanisms of (Bu2Se)-Se-t in the presence or absence of Me2Zn using deuterium labelled analogues", J MAT CHEM, 9(12), 1999, pp. 3005-3014

Abstract

Thermal decomposition of (Bu2Se)-Se-t in helium produces 2-methylpropene and 2-methylpropane (8 : 1) and no volatile selenium containing products, apart from the element. In hydrogen, the products are the same (8 : 1 ratio of 2-methylpropene : 2-methylpropane). However, the 2-methylpropane producedby decomposing d(18)-(Bu2Se)-Se-t in H-2 contains significant amounts of hydrogen (d(9) : d(10) = 2.6 : 1). In the codecomposition of d(0)- and d(18)-(Bu2Se)-Se-t in helium, d(0), d(1), d(9) and d(10)-2-methylpropane are allformed, but d(9)-(Bu2Se)-Se-t is not a product. Photolysis of d(0)- and d(18)-(Bu2Se)-Se-t in helium at room temperature produces 2-methylpropane and2-methylpropene (1 : 1) with the 2-methylpropane being d(0), d(1), d(9) and d(10). d(9)-(Bu2Se)-Se-t is also formed along with small amounts of 2,2,3,3-tetramethylbutane and d(0)- and d(18)-(Bu2Se2)-Se-t. Thermal codecomposition of Me2Zn with d(18)-(Bu2Se)-Se-t in H-2 produces d(0) and d(1)-methaneand d(8)-2-methylpropene together with traces of d(8)-2-methylpropane. These results are interpreted as indicating that thermally, (Bu2Se)-Se-t decomposes via homolytic cleavage of the Se-C bonds and that the free Bu-t .so formed initiates a radical chain reaction involving H-. as the chain carrier through its reaction with intact (Bu2Se)-Se-t to give hydrogen, 2 x 2-methylpropene, Se and H-.. The chain is initiated by Bu-t . abstracting H-. from (Bu2Se)-Se-t or from H-2. Semi-empirical calculations carried out with a variety of levels of theory have confirmed that E-C bond cleavage is the first step in the decomposition of all the group 16 precursors studied and have been used to model the product distribution with time. They confirmthe conclusions drawn on the basis of our experimantal observations, except that the H-. abstraction reactions from intact (Bu2Se)-Se-t probably do not occur by a concerted pathway, rather they are stepwise. The radical chain process also occurs in the presence of Me2Zn, but the radical chain initiator in this case is Me-. from homolytic fission of the Zn-C bonds. Evidence is presented that these reactions occur on the ZnSe surface. The small amount of 2-methylpropane produced from reaction of Me2Zn with (Bu2Se)-Se-t in H-2 comes from hydrogenation of 2-methylpropene catalysed by ZnSe. Photochemically, homolytic cleavage of the Se-C bonds in (Bu2Se)-Se-t again occurs, but (BuSe.)-Se-t has sufficient lifetime to recombine with Bu-t(.) and the major hydrocarbon products are formed from radical-radical reactions.

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Documento generato il 23/09/20 alle ore 06:12:20