  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.
