Collisional quenching of excited vinylidene (3B2) radicals

Abstract

Rate constants for the removal of excited-state vinylidene D/sub 2/CC (/sup 3/B/sub 2/) in the presence of He, Ar, N/sub 2/, H/sub 2/, CO, and CH/sub 4/ are reported at room temperature. The excited vinylidene radicals are generated via vacuum-ultraviolet photolysis of mixtures of C/sub 2/D/sub 3/Cl in the quencher gases through the reaction sequence C/sub 2/D/sub 3/Cl..-->..C/sub 2/D/sub 3/Cl*; C/sub 2/D/sub 3/Cl*..-->..D/sub 2/CC(/sup 3/B/sub 2/) + DCl. Excited triplet vinylidene radicals are then collisionally quenched to the singlet ground state which undergoes rapid isomerization to acetylene. Rate constant for removal of D/sub 2/C (/sup 3/B/sub 2/) by quenchers are determined by observation of the time-resolved absorption of either D/sub 2/CC(/sup 3/B/sub 2/) at 137 nm or product C/sub 2/D/sub 2/ at 151 nm. The observed quenching rate constants for the deuterated species are k/sub He/ = (1.9 +/- 0.3) x 10/sup -15/, k/sub Ar/ = (6.64 +/- 0.3) x 10/sup -15/, k/sub N/sub 2// = (8.5 +/- 0.2) x 10/sup -15/, k/sub H/sub 2// = (33.8 +/- 6.1) x 10/sup -15/, k/sub CO/ = (28.0 +/- 8.0) x 10/sup -15/, and k/sub CH/sub 4// = (28.0 +/- 8.0) x 10/sup -15/ cm/sup 3/ molecule/sup -1/ s/sup -1/. No evidencemore » for chemical reaction could be observed. The derived quenching cross sections are correlated with the potential well depth model. This correlation is valuable in predicting nonreactive collisional cross sections for additional gases.« less