Collisional Quenching of C2(d3Πg) and C$_{3}(\tilde{A}^{1}\Pi_{u})$ and Its Application to the Estimation of Absolute Particle Density in Laser-Ablation Carbon Plumes

Collisional quenching of laser-excited C-2(d(3)Pi(g)) and C-3((A) over tilde (1)Pi(a)) has been investigated experimentally(all in carbon plumes produced by laser ablation of a graphite target in ambient He gas. The radiative lifetime of C-2(d(3)Pi(g)) was evaluated to be 115 ns. Collision with He did not affect the lifetime of C-2(d(3) Pi(g)) at pressures less than 5 Torr, On the other hand collision with He reduced the lifetime of C-3(<()over tilde>) at pressures higher than 0.5 Torr. The radiative lifetime of C-3((A) over tilde (1) Pi(u)) and the rate coefficient for the collisional quenching were evaluated to be 210ns and 3.0 x 10(-11) cm(3)/s. repectively. Several microseconds after the irradiation of the ablation laser pulse, collision with particles ejected front the target reduced the lifetimes of both C-2(d(3)Pi(g)) and C-3((A) over tilde (1)Pi(a)). From the reduced lifetime of C-3((A) over tilde (1) Pi(a)) we estimated the absolute particle density in the plume.