Oriented xenon hydride molecules in the gas phase

Abstract

The production of the xenon hydride molecules HXeX with X = I and Cl in the gas phase is reviewed. These molecules are generated by the photolysis of the hydrogen halide HI and HCl molecules on the surface of large xenon Xe n clusters. Molecular dynamics simulations show that the flexible H atoms react with the heavy XeX moiety and form the desired molecules with nearly no rotational motion. They are observed by photodissociation with subsequent detection of the kinetic energy of the H atom fragment. During the generating process, the cluster starts to evaporate and the hydride molecule is left essentially free. For further discrimination against the H atom fragments from HX, the HXeX molecules are oriented in a combined pulsed laser field and a weak electrostatic field. The three topics which represent the background of our experiments are briefly reviewed: the nature and generation of rare gas hydrides, the alignment and orientation of molecules in electric fields, and the photodissociation of selected molecules in rare gas clusters. The conditions for detecting them in the gas phase are discussed. This is the trade off between the stability, which requires high electron affinity, and the conditions for orientation, which necessitate large polarizability anisotropies and dipole moments. Finally the prospects of detecting other classes of molecules are discussed. Contents page 1. Introduction 584 2. Background information 586 2.1. Rare gas hydride compounds 586 2.2. Orientation of molecules 588 2.3. Photodissociation of molecules in clusters 591 3. Experimental 594 4. Formation and orientation of the molecules 597 5. Results 599 5.1. Results for HXel 604 5.2. Results for HXeCl 604 5.3. Other molecules 607 6. Summary and prospects 609 Acknowledgments 610 References 611