Alrik J. van den Brom

State-to-state photodissociation of OCS (nu(2)=0,1 vertical bar JlM). I. The angular recoil distribution of CO (X (1)Sigma(+);v=0 vertical bar J)

State-to-state photodissociation experiments of OCS at 230 nm are reported using hexapole state selection of the parent molecule and velocity map ion imaging of the angular recoil of the CO photofragment. The role of the initial rovibrational state (ν2=0,1|JlM) of OCS on the angular recoil distribution is investigated. The CO (X 1Σ+;v=0|J) rotational distribution as well as the angular recoil anisotropy parameter β of the CO photofragment are reported for dissociation of single rovibrational (ν2=0,1|JlM) quantum states of OCS. A strong dependence of the anisotropy parameter β on the initial bending state, ν2=0 or 1, of OCS is observed. The effects of the initial bending state of OCS are rationalized in terms of the strong angular dependence of the transition dipole moment function of OCS for the 1 1Σ−(1 1A″) and 1 1Δ(2 1A′) excited state surfaces involved in the dissociation at 230 nm. The state-to-state imaging experiment provides a revised and improved determination of the binding energy of OCS (ν1,ν2,ν...

The correlation between 1(P-2(3/2))/I(P-2(1/2)) branching and CH3 rotation in photolysis of single quantum state-selected CH3I (JK=11)

Abstract The dependence of the I ( 2 P 3/2 )/ I ( 2 P 1/2 ) branching ratio on the end-over-end rotational state of the methyl photofragment, CH 3 (ν 2 =2|N,K=1) , after photodissociation at 266 nm of single quantum state-selected CH 3 I (JK=11) molecules is reported. Using velocity map imaging the spatial velocity distribution of the vibrationally excited CH 3 ( ν 2 =2) photofragment was detected. The I ( 2 P 3/2 ) and I ( 2 P 1/2 ) yields were extracted from the speed distribution of rotationally selected CH 3 (ν 2 =2|N,K=1) photofragments. Quantitative analysis shows a strongly increasing I ( 2 P 3/2 )/ I ( 2 P 1/2 ) branching ratio with increasing CH 3 end-over-end rotational motion, in reasonable agreement with recent three-dimensional state-to-state ab initio calculations.

Photodissociation of laboratory oriented molecules: Revealing molecular frame properties of nonaxial recoil

We report the photodissociation of laboratory oriented OCS molecules. A molecular beam of OCS molecules is hexapole state-selected and spatially oriented in the electric field of a velocity map imaging lens. The oriented OCS molecules are dissociated at 230 nm with the linear polarization set at 45 degrees to the orientation direction of the OCS molecules. The CO(nu=0,J) photofragments are quantum state-selectively ionized by the same 230 nm pulse and the angular distribution is measured using the velocity map imaging technique. The observed CO(nu=0,J) images are strongly asymmetric and the degree of asymmetry varies with the CO rotational state J. From the observed asymmetry in the laboratory frame we can directly extract the molecular frame angles between the final photofragment recoil velocity and the permanent dipole moment and the transition dipole moment. The data for CO fragments with high rotational excitation reveal that the dissociation dynamics is highly nonaxial, even though conventional wisdom suggests that the nearly limiting beta parameter results from fast axial recoil dynamics. From our data we can extract the relative contribution of parallel and perpendicular transitions at 230 nm excitation.

Molecular and laboratory frame photofragment angular distributions from oriented and aligned molecules

We present explicit expressions for the molecular frame and laboratory frame photofragment angular distributions from oriented parent molecules, in terms of the dynamically significant molecular frame angles between the recoil direction and the transition and permanent dipole moments of the molecule. We discuss how these angles can be measured from distinct experimental geometries. Explicit examples are given on the extracted information of the molecular frame photodissociation, especially in case of non-axial recoil dynamics.

State-to-state photodissociation of carbonyl sulfide (nu2=0,1/JlM). II. The effect of initial bending on coherence of S(1D2) polarization.

Photodissociation studies using ion imaging are reported, measuring the coherence of the polarization of the S((1)D(2)) fragment from the photolysis of single-quantum state-selected carbonyl sulfide (OCS) at 223 and 230 nm. A hexapole state-selector focuses a molecular beam of OCS parent molecules in the ground state (nu2=0mid R:JM=10) or in the first excited bending state (nu2=1mid R:JlM=111). At 230 nm photolysis the Im[a1 (1)(parallel, perpendicular)] moment for the fast S(1D2) channel increases by about 50% when the initial OCS parent state changes from the vibrationless ground state to the first excited bending state. No dependence on the initial bending state is found for photolysis at 223 nm. We observe separate rings in the slow channel of the velocity distribution of S(1D2) correlating to single CO(J) rotational states. The additional available energy for photolysis at 223 nm is found to be channeled mostly into the CO(J) rotational motion. An improved value for the OC-S bond energy D0=4.292 eV is reported.

State-to-state photodissociation of carbonyl sulfide ({nu}{sub 2}=0,1|JlM). II. The effect of initial bending on coherence of S({sup 1}D{sub 2}) polarization

Photodissociation studies using ion imaging are reported, measuring the coherence of the polarization of the S((1)D(2)) fragment from the photolysis of single-quantum state-selected carbonyl sulfide (OCS) at 223 and 230 nm. A hexapole state-selector focuses a molecular beam of OCS parent molecules in the ground state (nu2=0mid R:JM=10) or in the first excited bending state (nu2=1mid R:JlM=111). At 230 nm photolysis the Im[a1 (1)(parallel, perpendicular)] moment for the fast S(1D2) channel increases by about 50% when the initial OCS parent state changes from the vibrationless ground state to the first excited bending state. No dependence on the initial bending state is found for photolysis at 223 nm. We observe separate rings in the slow channel of the velocity distribution of S(1D2) correlating to single CO(J) rotational states. The additional available energy for photolysis at 223 nm is found to be channeled mostly into the CO(J) rotational motion. An improved value for the OC-S bond energy D0=4.292 eV is reported.

Slice imaging of photodissociation of spatially oriented molecules

An electrostatic ion lens to spatially orient parent molecules and to image the angular distribution of photofragments is presented. Photodissociation of laboratory-oriented molecules makes it possible to study the dynamics of the dissociation process in more detail compared to photodissociation of nonoriented molecules. Using the velocity map imaging technique in combination with the slice imaging technique, the spatial recoil distribution of the photofragments can be measured with high resolution and without symmetry restrictions. Insertion of orientation electrodes between the repeller and the extractor of a velocity mapping electrostatic lens severely distorts the ion trajectories. The position where the ions are focused by the lens, the focal length, can be very different in the directions parallel and perpendicular to the inserted orientation electrodes. The focal length depends on the exact dimensions and positions of the electrodes of the ion lens. As this dependence is different in both direction...