Absolute absorption cross-section measurements of CO2 in the ultraviolet from 200 to 206 nm at 295 and 373 K

Laboratory measurements of the absolute absorption cross-section of CO 2 at the temperatures 295 and 373 K have been made between 200 and 206 nm using cavity ring-down spectroscopy. Below 205 nm, the cross-section at 373 K is significantly larger than at 295 K, whereas beyond 205 nm measurements at both temperatures yield cross-sections approximately equal to the Rayleigh scattering cross-section, within experimental error. The present measurements should resolve a long-standing discrepancy between previously published data on this system. © 2004 Elsevier B.V. All rights reserved

Impulsive orientation and alignment of quantum-state-selected NO molecules

Manipulation of the molecular-axis distribution is an important ingredient in experiments aimed at understanding and controlling molecular processes(1-6). Samples of aligned or oriented molecules can be obtained following the interaction with an intense laser field(7-9), enabling experiments in the molecular rather than the laboratory frame(10-12). However, the degree of impulsive molecular orientation and alignment that can be achieved using a single laser field is limited(13) and crucially depends on the initial states, which are thermally populated. Here we report the successful demonstration of a new technique for laser-field-free orientation and alignment of molecules that combines an electrostatic field, non-resonant femtosecond laser excitation(14) and the preparation of state-selected molecules using a hexapole(2). As a unique quantum-mechanical wavepacket is formed, a large degree of orientation and alignment is observed both during and after the femtosecond laser pulse, which is even further increased (to < cos theta > = -0.74 and < cos(2)theta > = 0.82, respectively) by tailoring the shape of the femtosecond laser pulse. This work should enable new applications such as the study of reaction dynamics or collision experiments in the molecular frame, and orbital tomography(11) of heteronuclear molecules.No Full Tex

Strong laser field control of fragment spatial distributions from a photodissociation reaction

The notion that strong laser light can intervene and modify the dynamical processes of matter has been demonstrated and exploited both in gas and condensed phases. The central objective of laser control schemes has been the modification of branching ratios in chemical processes, under the philosophy that conveniently tailored light can steer the dynamics of a chemical mechanism towards desired targets. Less explored is the role that strong laser control can play on chemical stereodynamics, i.e. the angular distribution of the products of a chemical reaction in space. This work demonstrates for the case of methyl iodide that when a molecular bond breaking process takes place in the presence of an intense infrared laser field, its stereodynamics is profoundly affected, and that the intensity of this laser field can be used as an external knob to control it.Peer Reviewe