QUENCHING OF PF(B(1)SIGMA(-2, BR-2, NO2, AND N2O - THE ENERGY-POOLINGREACTION WITH NF(B1-SIGMA+) AND THE THERMOCHEMISTRY OF PF, PCL AND PBR()) BY F2, CL)

Reactive quenching of PF(b(1) Sigma(+)) molecules by F-2, Cl-2, and Br -2 has been studied at 300 K in a flow reactor. The PF(b) molecules we re generated by a passing a dilute flow of PF3 in He through a de disc harge. The total removal rate constants for PF(b) by F-2, Cl-2, Br-2, and NO2 are 2.1 x 10(-11), 8.1 x 10(-12), 2.3 x 10(-10) and 6.8 x 10(- 11) cm(3) molecule(-1) s(-1), respectively. Quenching by N2O is much s lower and probably proceeds by an electronic-to-vibrational energy tra nsfer mechanism. The reactions of PF(b(1) Sigma(+)) with Cl-2 and Br-2 proceed, in part, to give PCl(b(1) Sigma(+)) and PBr(b(1) Sigma(+)), respectively. The large rate constants for F-2 and NO2 suggest that th e quenching mechanism could be chemical reactions, even though the pro ducts have not been identified. The thermochemistry associated with PC l(b(1) Sigma(+)) and PBr(b(1) Sigma(+)) formation shows that D-0(P-F) is no more than 6.9 and 18.0 kcal mol(-1) larger than D-0(P-Cl) and D- 0(P-Br), respectively. Formation of PF(A(3)II) by the energy-pooling r eaction of PF(b(1) Sigma(+)) with NF(b(1) Sigma(+)) was observed. The estimated PF(b) and NF(b) concentrations indicate that the PF(A) forma tion rate constant is large and this energy-pooling reaction seems to be efficient.