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Both single-laser and two-laser experiments were conducted to look into the ion-imaging of Br*(2P1/2) and Br(2P3/2) photo-fragmented from 1-bromo-2-methylbutane in the range 232-240 nm via a detection scheme of (2+1) resonance-enhanced multiphoton ionization. The angular analysis of these photofragment distributions yields the anisotropy parameter beta = 1.88 +/- 0.06 for the Br* excited state which arises from a parallel transition, while beta = 0.63 +/- 0.09 for the Br ground state indicates the contribution from both a perpendicular transition and a non-adiabatic transition. When a hexapole coupled with an orienting field was implemented, the parent molecules are spatially oriented to yield an orientation efficiency || of 0.15. Besides the chi angle between the recoil velocity v and the transition dipole moment mu, orienting molecules allows for the evaluation of the angle alpha between v and the permanent molecular dipole moment d. The angular analysis of Br* photofragment distribution yields chi to be 11.5 degrees and alpha in the range from 160 degrees to 180 degrees with weak dependency. In the two-laser experiments, the angular anisotropy of Br photofragment distribution was found to be smaller (0.38 +/- 0.10) when the photolysis wavelength was red-shifted to 240 nm, suggesting the increasing contributions from perpendicular transitions., Comment: 36 pages, 7 figures

A new type of, called stereo-specific entangled, roaming mechanism is presented in the reaction of structurally unstable B5 cluster with the hydrogen atom, by using the direct ab initio trajectory calculation with a practical level of DFT method using the rang-separated functional. In this mechanism, the light moiety, i.e. H roams around far from the B5 cluster caused by a stereo-specific energy transfer of translational energy to the cluster vibrational energy through the direct coupling due to the large amplitude motion of the unstable B5 cluster. We confirmed by the comparative computation that a clear change occur from the roaming trajectory to the repulsive trajectory, when we froze the vibrational motion of the B5 cluster. This drastic change of the trajectory due to the change between the structurally unstable B5 cluster and the frozen B5 cluster revealed the importance of kinematic energy transfer resulted in the soft-landing-like hydrogen absorption which manifested the present stereo-specific entangled roaming mechanism. The trajectory calculation revealed that the present new type of roaming mechanism is very sensitive to the azimuthal angle of the H atom attack, especially to the bisection of the B-B bond of the B5 cluster, where the energy flow from relative kinetic energy to the vibrational energy of the cluster efficiently takes place through the roaming trajectory driven due to the structural fluctuation of the B5 cluster., Comment: Key Words: Stereo-specific internally entangled roaming mechanism, structurally unstable B5 cluster, the ab initio trajectory dynamics, coupling of the kinematic motion with the cluster bond frustration, soft-landing hydrogen absorption by the B5 cluster

Molecular orientation is a fundamental requisite in the study of stereodirected dynamics of collisional and photoinitiated processes. In this last decade, variable hexapolar electric filters have been developed and employed for the rotational-state selection and the alignment of molecules of increasing complexity, for which main difficulties are their mass, their low symmetry and the very dense rotational manifold. In this work, for the first time, a complex molecule such as 2-bromobutane, an asymmetric-top containing a heavy atom (the bromine), has been successfully oriented by a weak homogeneous field placed downstream the hexapolar filter. Efficiency of the orientation has been characterized experimentally, by combining time-of-flight measurements and a slice-ion-imaging detection technique. The application is described to the photodissociation dynamics of the oriented 2-bromobutane, which was carried out at a laser wavelength of 234 nm, corresponding to the breaking of the C Br bond. The Br photofragment is produced in both the ground Br (2P3/2) and the excited Br (2P1/2) electronic states and both channels are studied by the slice imaging technique, revealing new features in the velocity and angular distributions with respect to previous investigations on non-oriented molecules.

Hexapole oriented 2-bromobutane is photodissociated and detected by a slice ion imaging technique at 234 nm. The laser wavelength corresponds to the C Br bond breaking with emission of a Br atom fragment in two accessible fine structure states: the ground state Br and the excited state Br*, both observable separately by resonance enhanced multiphoton ionization (REMPI). Orientation is evaluated by time of flight measurements combined with slice ion imaging., Comment: 4 pages, 2 figures, conference paper

Electrostatic hexapoles are revealed as a powerful tool in the rotational state-selection and alignment of molecules to be utilized in beam experiments on collisional and photoinitiated processes. In the paper, we report results on the application of the hexapolar technique on the recently studied chiral molecules propylene oxide, 2-butanol and 2bromobutane, to be investigated in selective photodissociation and enantiomeric discrimination., Comment: 4 pages, 2 figures, conference