Photodissociation stereodynamics of organic halides and halogen molecules

Abstract

Stronger avoided curve crossing between the $A_1$ and $B_1$ states in the $CF_2Br_2$ photolysis at 234 and 265 nm The photodissociation dynamics of $CF_2Br_2$ were studied using a two-dimensional photofragment ion image technique at two wavelengths 234 and 265 nm. At 234 nm, three dissociation channels, i.e., the radical, $CF_2Br$ + $Br(^2P_J)$(J=1/2, 3/2), the three body, $CF_2$ + $2Br(^2P_J$) (J=1/2, 3/2), and the molecular elimination channel, $CF_2$ + $Br_2$, were observed with quantum yields of 0.84, 0.15 and trace, respectively. The difference between $β_{CF_2Br+Br(^2P_{3/2})}=0.65$ and $β_{CF_2Br+Br(^2P_{1/2})}=0.80$ suggests that the excited $A_1$ and $B_1$ states are strongly correlated by avoided curve crossing with a probability of 0.78. At 265 nm, the radical channel, the only observed primary dissociation channel, shows several components due to the transition close to the curve crossing point. On the basis of observations at both wavelengths, we have proposed a photodissociation dynamics model of $CF_2Br_2$ after A-band excitation. $Br(^2P_J)$ and $Cl(^2P_J)$ atom formation dynamics of allyl bromide and chloride at 234 nm Photodissociation dynamics of allyl bromide and chloride have been investigated at 234 nm using two-dimensional photofragment ion image technique coupled with [2+1] resonance-enhanced multiphoton ionization scheme. After absorbing a photon, allyl bromide dissociates into $C_3H_5$ + $Br(^2P_J; J=1/2, 3/2)$ exclusively via the repulsive surfaces. Intensity borrowing from the nearby $^1(π, π^*)$ state is attributed to the enhanced contribution of the singlet state to the initial transition. Trimodal translational energy distributions of $Cl(^2P_J; J=1/2, 3/2)$ have been observed after the photolysis of allyl chloride. Low-velocity components with Boltzmann shapes are produced via the internal conversion between the initially pumped $^1(π, π^*)$ state and vibrationally excited ground state. Middle-velocity components with Gaussian...