This book explains the theory and methods by which gas molecules can be polarized by light, a subject of considerable importance for what it tells us about the electronic structure of molecules and properties of chemical reactions. Starting with a brief review of molecular angular momentum, the text goes on to consider resonant absorption, fluorescence, photodissociation and photoionization, as well as collisions and static fields. A variety of macroscopic effects are considered, among them angular distribution and the polarization of emitted light, ground state depopulation, laser-induced dichroism, the effect of collisions and external magnetic and electric field effects. Most examples in the book are for diatomic molecules, but symmetric-top polyatomic molecules are also included. The book concludes with a short appendix of essential formulae, tables for vector calculus, spherical functions, Wigner rotation matrices, Clebsch-Gordan coefficients, and methods for expansion over irreducible tensors.

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The K and Cs atom pair and its X 1 + and a 3 + electronic molecular states are studied by Fourier-transform spectroscopy with special emphasis on bound states close to the ground state asymptote (4s)K + (6s)Cs. Significant vibrational mixing due to hyperfine coupling was observed leading to improved potential energy curves for both states. The observed intensity pattern of the hyperfine structure for the last vibrational levels of X 1 + and a 3 + reveals deep insight into the multicomponent wave function of such levels with its influence for modeling the asymptotic behavior of the excited electronic states involved in the reported observations. Examples of derived properties of cold collisions are given and the importance of the present results for efficient production schemes for ultracold KCs is discussed.

The coupling of the X 1 + and a 3 + states of the atom pair Na + Cs and modelling cold collisions

The X 1 Σ + state of NaRb was studied by Fourier transform spectroscopy. An accurate potential energy curve was derived from more than 8800 transitions in isotopomers 23 Na 85 Rb and 23 Na 87 Rb. This potential reproduces the experimental observations within their uncertainties of 0.003 cm −1 to 0.007 cm −1 . The outer classical turning point of the last observed energy level (v ′′ = 76, J ′′ = 27) lies at ≈ 12.4 Å, leading to a energy of 4.5 cm −1 below the ground state asymptote.