QUENCHING RATE CONSTANTS FOR NCL(B (1)SIGMA(+)) AND PCL(B (1)SIGMA(+)) AND RADIATIVE LIFETIMES OF NCL(B(1)SIGMA(+)), PCL(B(1)SIGMA(+)) AND PBR(B(1)SIGMA(+))

NCl(b (1) Sigma(+)), PCl(b (1) Sigma(+)) and PBr(b (1) Sigma(+)) molec ules have been generated in a flow reactor by passing dilute flows of NFCl2, PCl3 and PBr3 in He through a de discharge, and the total rate constants for quenching of NCl(b (1) Sigma(+)) and PCl(b (1) Sigma(+)) by several diatomic and small polyatomic molecules have been measured at 300 K. Except for O-2, NO2 and molecular halogens, the rate consta nts are in the 10(-13)-10(-14) cm(3) molecule(-1) s(-1) range. The dep endence of the rate constants on the properties of the reagent suggest s that the dominant quenching mechanism for PCl(b) and NCl(b) is elect ronic-to-vibrational (E-V) energy transfer with the a (1) Delta state as the product, just as for the reactions of NF(b (1) Sigma(+)) and PF (b (1) Sigma(+)). The rate constants for quenching of NCl(b (1) Sigma( +)) and PCl(b (1) Sigma(+)) by O-2 are 1.0 x 10(-12) and less than or equal to 10(-15) cm(3) molecule(-1) s(-1), respectively, and are in ac cord with an electronic-to-electronic (E-E) energy transfer with the f inal states being O-2(b (1) Sigma(+)) + NCl(X (3) Sigma(-)) or PCl(X ( 3) Sigma(-)). Formation of PBr(b (1) Sigma(+)) from the PCl(b (1) Sigm a(+)) + Br-2 reaction was observed, and quenching of PCl(b (1) Sigma()) by F-2, Cl-2 and Br-2 proceeds by a chemical mechanism with rate co nstants of 2.3 x 10(-12), 0.79 x 10(-12) and 16 x 10(-12) cm(3) molecu le(-1) s(-1), respectively. The radiative lifetimes for NCl(b (1) Sigm a(+)), PCl(b (1) Sigma(+)) and PBr(b (1) Sigma(+)) are 2.0 +/- 0.4, 4. 9 +/- 0.8 and 0.8 +/- 0.2 ms, respectively, as determined from the dec ay of the respective b (1) Sigma(+) --> X (1) Sigma(-) emission intens ities along the flow reactor.