Book contents
- Frontmatter
- Contents
- 0 Introduction
- 1 Rotational relaxation
- 2 Orientational relaxation in dense media
- 3 Transformation of isotropic scattering spectra
- 4 Quantum theory of spectral collapse
- 5 Rotational relaxation: kinetic and spectral manifestations
- 6 Impact theory of orientational relaxation
- 7 Rotation and libration in a fluctuating cell
- Appendix 1
- Appendix 2
- Appendix 3
- Appendix 4
- Appendix 5
- Appendix 6
- Appendix 7
- Appendix 8
- Appendix 9
- References
- Index
2 - Orientational relaxation in dense media
Published online by Cambridge University Press: 06 November 2009
- Frontmatter
- Contents
- 0 Introduction
- 1 Rotational relaxation
- 2 Orientational relaxation in dense media
- 3 Transformation of isotropic scattering spectra
- 4 Quantum theory of spectral collapse
- 5 Rotational relaxation: kinetic and spectral manifestations
- 6 Impact theory of orientational relaxation
- 7 Rotation and libration in a fluctuating cell
- Appendix 1
- Appendix 2
- Appendix 3
- Appendix 4
- Appendix 5
- Appendix 6
- Appendix 7
- Appendix 8
- Appendix 9
- References
- Index
Summary
Information on orientational relaxation may be obtained by a wide range of techniques. Dielectric relaxation and magnetic resonance, neutron and light scattering, infrared spectroscopy and fluorescence depolarization are widely used. These different experimental probes of the phenomenon characterize it in different ways. The advantage of spectroscopic investigations is that they give information on relaxation times as well as on the corresponding correlation functions and their spectra. In particular, by combining the information in an absorption spectrum with that obtained from Raman scattering, one can determine the two lowest correlation functions of a molecule's axis position. A complete description of orientational relaxation is given by the infinite set of these functions.
The orientation of linear rotators in space is defined by a single vector directed along a molecular axis. The orientation of this vector and the angular momentum may be specified within the limits set by the uncertainty relation. In a rarefied gas angular momentum is well conserved at least during the free path. In a dense liquid it is a molecule's orientation that is kept fixed to a first approximation. Since collisions in dense gas and liquid change the direction and rate of rotation too often, the rotation turns into a process of small random walks of the molecular axis. Consequently, reorientation of molecules in a liquid may be considered as diffusion of the symmetry axis in angular space, as was first done by Debye.
- Type
- Chapter
- Information
- Spectroscopy of Molecular Rotation in Gases and Liquids , pp. 59 - 91Publisher: Cambridge University PressPrint publication year: 1994