Photodissociation of CSCl2 at 235 nm: Kinetic energy distributions and branching ratios of Cl atoms and CSCl radicals

Abstract

The photodissociation dynamics of thiophosgene (CSCl 2) and the respective branching ratios of both dissociation products Cl and CSCl have been studied by 3D imaging of the photodissociation product chlorine in its ground state 2 P 3/2 ͓Cl͔ and excited spin-orbit state 2 P 1/2 ͓Cl*͔ employing the resonance enhanced multiphoton ionization and time-of-flight technique at a dissociation wavelength of about 235 nm. A novel technique is applied where the complete three-dimensional ͑3D͒ momentum vector of a reaction product is directly determined. The kinetic energy distribution ͑KED͒ for Cl* is observed for the first time. The obtained KEDs of Cl and Cl* are different in the low kinetic energy range due to the correlating state of the partner fragment CSCl. In the case of ground state Cl the CSCl partner radical is produced in the ground X , à , and B states with a contribution of 4Ϯ0.5%, 60Ϯ5%, and 36Ϯ3%, respectively. In the case of Cl* the corresponding CSCl is produced with a contribution of 7.5Ϯ0.5% in the ground X , 71.5Ϯ5.5% in state à , and 21Ϯ1.5% in state B. The yield of Cl*, (Cl*)ϭ P(Cl*)/͓ P(Cl)ϩ P(Cl*)͔, was found to be 0.47. No significant velocity dependence of the anisotropy parameter ␤ could be observed. The mean value ϩ0.03 suggests a decay on the B (A 1) surface.

Striving To Understand the Photophysics and Photochemistry of Thiophosgene: A Combined CASSCF and MR−CI Study

“…35 The present calculations indicate that S 2 dissociation to Cl(X ˜2P) + ClCS-(A ˜2A′′) is another important route for S 2 deactivation. In addition, the dominant ClCS fragment observed in the A ˜2A′′ excited state 28 indicates that S 2 C-Cl bond cleavage has some preference over S 2 f S 3 IC. This is consistent with the calculated result that TS(S 2 ) has lower energy relative to the S 3 /S 2 intersection.…”

“…The quantum yield of Cl production from Cl 2 CS was observed to be unity and pressure independent at excitation wavelengths shorter than 253.7 nm, which indicates that Cl 2 CS dissociation to ClCS + Cl is the only primary process and the dissociation must be direct . Recently, photodissociation dynamics of Cl 2 CS at 235 nm have been investigated employing the resonance-enhanced multiphoton ionization and time-of-flight technique …”

“…This was attributed to the crossing of the S 3 and S 2 electronic states at long C−S distance in several experimental studies. − The large C−S bond length in the S 3 state leads to very favorable FC factors for S 3 → S 0 IC. , If S 2 → S 3 IC followed by direct IC to the ground electronic state is the only route for S 2 deactivation at excess energies larger than 1700 cm -1 , the fragments are formed only in the ground state. However, it was found that the ClCS radicals are mainly produced in the excited electronic state upon photoexcitation of Cl 2 CS at 235 nm …”

“…The ClCS and Cl 2 fragments were detected by the 248 nm laser photolysis of a pulsed molecular beam of thiophosgene The photodissociation dynamics of Cl 2 CS at 235 nm have been studied by employing the resonance-enhanced multiphoton ionization and time-of-flight technique . It was found that Cl atoms and ClCS radicals were formed in the ground and excited states.…”

Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging

“…15 The latter technique has been used for several years now and has successfully been applied to a number of systems. [16][17][18][19][20][21][22][23][24][25] In the past couple of years it has become more and more widespread in the molecular dynamics community, 26,27 but a drawback of this technique has been so far the lower energy resolution compared to velocity map imaging, slice imaging, or the technique suggested by Vrakking, since these techniques make use of ion optics. The ion optics serve to compensate for the length of the excitation volume which smears out the velocity distribution in the direction of the laser beam, if a homogeneous field is applied und parallel ion trajectories are not focused onto one point.…”