Curve-Crossing Collisions of Excited Lead Atoms in Flames

T. J. Brady, L. F. Phillips
1981 Proceedings of the Royal Society A  
{Communicated by T. M. Sugden, S -Received 30 July 1 Lead atoms, present as a trace additive in a series of premixed H 2-N 2-0 2 flames, were excited to the 71 * 3P£ state by 405.8 nm radiation from a nitrogen-pum ped dye laser. R ate constants for spin-orbit relaxation to the 73Pg state were obtained separately for collisions with atomic hydrogen and for collisions with the bulk flame gas, by measuring the relative intensities of fluorescence a t 364.0 and 368.3 nm as a function of distance
more » ... m the reaction zone in each flame. For hydrogen atoms the rate constant is typically 1 x 10-9 cm3 molecule-1 s-1, decreasing with increasing tem perature; for the bulk flame gas the rate constant is typically 1 x 10~n cm3 molecule-1 s-1, increasing with increasing tem pera ture. Numerical calculations for model systems, with the use of Morse and L ennard-Jones potentials to describe the interaction of the colliding species, show th a t the negative tem perature coefficient found for atomic hydrogen can be attributed to the crossing of attractive potential curves, corresponding to bound excited states of PbH . [ 545 ] relaxation of P b(3P£) by bulk flame constituents (H2, N 2, H 20 ) has a positive tem perature coefficient. Excited lead atoms in flames 547 2. T h e o r y of the m et h o d 20 Vol. 376. A
doi:10.1098/rspa.1981.0107 fatcat:daah2shdrvdw5idzlifalxdmda