Photodissociation dynamics study using nonlinear spectroscopy

Abstract

Chlorine Atom Formation Dynamics of NOCl and $PCl_3$ at 222 nm: The dissociation dynamics of NOCl and ${ PCl}_3$ after UV photoexcitation at 222 nm have been investigated. Total and relative quantum yields of Cl($^{2}P_{3/2}$) and $Cl*(^{2}P_{1/2}$) atoms were determined using the laser photolysis/vacuum-UV laser-induced fluorescence technique. The total quantum yield for chlorine atom formation of $PCl_3$ was determined to be 0.76±0.13. The relative Cl* quantum yields were found to be 0.36 (NOCl) and 0.53 ($PCl_3$), respectively. The nearby triplet state, as well as the singlet state $S_5 (4^1A`)$, seems to contribute to the A band absorption of NOCl. It is concluded that the dissociation process of PCl3 yielding ground state $PCl_2$(${\tilde X}^{2}B_1$) and Cl/Cl* is dominant at 222 nm photolysis. Dynamics of the H+HCl reaction at 1.4 eV: The dynamics of the gas-phase H+HCl reaction has been investigated at an average center-of-mass collision energy of 1.4 eV. The laser photolysis/vacuum-UV laser-induced fluorescence technique coupled with a sum-difference frequency conversion scheme was employed to determine the absolute reaction cross-section for spin-orbit ground state Cl atom formation and the spin-orbit branching ratio between Cl and Cl*. A photolytic calibration method was used as a source for well-defined concentrations of Cl and Cl*. The absolute reaction cross-section has been found to be $σ_R^{Cl} (1.4eV) = 0.24±0.03 Å^2$. This coincides well with the theoretical predictions and other experimental observations. Small but apparent signal of Cl* from the reaction was observed, leading to the branching ratio of $β _{Cl*} = 0.07±0.01$. This implies that the nonadiabatic transition leading to Cl* formation in the exit channels of the exchange reaction is not negligible at high collision energies. Detection of OH Radicals in a Butane/Air Flame: DFWM has been employed to detect OH radicals in a butane/air flame. The fully resonant wave-coupling process...