THE CU+F(2) CHEMILUMINESCENT REACTION REVISITED .2. KINETIC-STUDIES

Optical pumping, with a copper vapor laser, has been used to state select ground S-2(1/2) and metastable 2D5/2 and 2D3/2 copper atoms in a fast flow, low pressure reactor combined with a hollow cathode sputtering source. The absolute densities of these atoms (around 2 X 10(11) and 10(9) atoms cm-3 for 2S and 2D, respectively) were measured by resonant absorption and laser induced fluorescence techniques. Their isolated reactions with F2 have been studied in detail at 300 K. The total reaction cross section for Cu(2S) is almost four times larger than for Cu*(2D) metastable atoms. The strong chemiluminescent emission from electronically excited CuF* formed is attributed to the reaction of metastable Cu*(2D) atoms, the Cu(2S) reaction leading directly to ground state CuF(X1SIGMA+) molecules. Spectral analysis of the chemiluminescence shows a highly inverted vibrational distribution in all energetically accessible excited states: a 3SIGMA+, b3PI, B1SIGMA+, C1PI, and D3DELTA1 of CuF with [f(v)] almost-equal-to 0.7. Branching ratios for formation of the molecules in these states have been determined for reaction of copper atoms in each of the three electronic states. From the highest vibrational levels populated by reaction of Cu* (2D5/2) with F2, v(max) = 21 and 26 for C1PI and b3PI states, respectively, one can deduce a more precise value of 33 560 +/- 240 cm-1 for the dissociation energy of the ground state CuF(X 1SIGMA+). The strong propensity observed for formation of CuF*(a,b,B,C,D) by Cu*(2D,3d(9)4s2) +F2 and CuF(X1SIGMA+) by Cu(2S,3d(10)4s)+F2 reactions can be explained by conservation of the copper atom ionic core throughout the course of the reaction.