Molecular spectroscopy: Where theory
meets experiment
Kenneth Ruud
Centre for Theoretical and Computational Chemistry
Department of Chemistry
University of Tromsø—The Arctic University of Norway, N-9037 Tromsø,
Norway
By considering the interactions between the molecular electronic structure
and external electric and magnetic fields, as probed in a wide range of
experimental spectroscopic techniques, a detailed understanding of the electronic
structure of molecules can be obtained. Spectroscopy represents a direct
link between the experimental observation of a molecule and electronicstructure
calculations. By computing experimental spectra, including all
possible effects, accurate, high-resolution experimental spectra can provide
a very stringent test of the quality of a computational method and thus its
description of the electronic structure of the molecule.
Simultaneously, theory can in many cases provide additional insight into
the origin of experimentally observed spectra, assuming that we are able to
calculate all the processes and interactions that are involved in the experimental
measurement. Together, theoretical and computational spectroscopy
can provide unique and detailed insight into the molecular responses to electromagnetic
field.
In this talk, I will outline the principles for calculating molecular properties
for any element of the periodic table. A particular focus will be on the
calculation of the nuclear magnetic shielding constants of nuclear magnetic
resonance (NMR) spectroscopy, which describes the coupling between the
nuclear magnetic moment and an external magnetic field. I will in particular
focus on the use of NMR to determine absolute shielding constants and
nuclear magnetic dipole moments.
If time allows, I will also give some recent examples from our work on
multiphoton spectroscopy both in the electronic and vibrational frequency
range.