QUENCHING RATE CONSTANTS OF NF(A DELTA-1) AT ROOM-TEMPERATURE

The gas-phase quenching rate constants for NF(a1Δ) have been measured at 300 K for 60 reagent molecules. The experiments were done in a Pyrex glass flow reactor coated with halocarbon wax using the 2F + HN3 reaction as a source of NF(a1Δ). The rate constants span a wide range of values; the rate constants for most diatomic molecules are less than 1 × 10-14 cm3 molecule-1 s-1, but more reactive molecules, such as C2H4, NH3, or P(CH3)3, have rate constants near 10-11 cm3 molecule-1 s-1. For polyatomic reagents that can act as Lewis bases, a correlation was found between the magnitude of the quenching rate constant and the base strength (measured as the proton affinity) of the molecule, which is evidence that the closed-shell (πx2-πy2) component of the NF(a1Δ) state is involved in the quenching. The rate constants for NF(a1Δ) are larger than for the analogous O2(a1Δ) state because of the more attractive interaction potentials between NF(a) and stable reagent molecules. A few experiments were done at ∼200 K to demonstrate that this NF(a) source is suitable for low-temperature studies; the rate constants for O2, CO, and C2H4 decreased with reduction in temperature. The 300 K bimolecular self-removal rate constant for NF(a1Δ) was assigned as (5 ± 2) × 10-12 cm3 molecule-1 s-1; bimolecular energy pooling by NF(a) to give NF(b) is not an important quenching pathway. Quenching of NF(a) by F atoms has a small rate constant, (4 ± 2) × 10-13 cm3 s-1. © 1990 American Chemical Society.