Contemporary research in atomic and molecular physics concerns itself with studies of interactions of electron, positron, photons, and ions with atoms, molecules, and clusters; interactions of intense ultrashort laser interaction with atoms, molecules, and solids; laser assisted atomic collisions, optical, and magnetic traps of neutral atoms to produce ultracold and dense samples; high resolution atomic spectroscopy and experiments by using synchrotron radiation sources and ion storage rings. In recent years, important advances have been made in the experimental as well as theoretical understanding of atomic and molecular physics. The advances in atomic and molecu lar physics have helped us to understand many other fields, like astrophyics, atmo spheric physics, environmental science, laser physics, surface physics, computational physics, photonics, and electronics. XII National Conference on Atomic and Molecular Physics was held at the Physics Department, M. 1. S. University, Udaipur from 29th Dec. 1998 to 2ndJan. 1999 under the auspices of the Indian Society of Atomic and Molecular Physics. This volume is an outcome of the contributions from the invited speakers at the conference. The volume contains 24 articles contributed by the distinguished scientists in the field. The contrib utors have covered a wide range of topics in the field in which current research is being done. This also reflects the trend of research in this field in Indian universities and research institutes. We are grateful to the national programme committee, national, and local organiz ing committees, and members of the Physics Department and Computer Centre, M. 1.