Introduction to Modeling High‐resolution Spectra

The basic principles of electronic spectroscopy of atoms and molecules in the gas phase are presented. In the first part, the elementary concepts necessary to describe the electronic structure of atoms, diatomic molecules, and polyatomic molecules are introduced in a systematic manner, with an effort to classify the different interactions (electrostatic, spin–orbit, hyperfine) and types of motions (electronic, vibrational, rotational), which determine the energy level structures. In the second part, electronic transitions are discussed, with their spin‐rovibrational structures. Examples ranging from the simple band structure of \documentclass{article}\usepackage{amsmath}\usepackage{amssymb}\usepackage{amsbsy}\pagestyle{empty}\begin{document}$\rm{\Sigma}^{+}_{{{\rm u}}}\leftarrow \rm{\Sigma}_{{{\rm g}}}^{+}$\end{document} electronic transitions of homonuclear diatomic molecules to the highly complex band structure of polyatomic molecules subject to strong vibronic interactions are used to illustrate the richness of electronic spectra.

Section: Angular Momentum Coupling Case (E)mentioning

confidence: 99%

Fundamentals of Electronic Spectroscopy

Wörner

Merkt

2011

Fundamentals of Rotation–Vibration Spectra

Albert

Hollenstein

et al. 2011

We provide a survey of fundamental aspects of rotation-vibration spectra. A basic understanding of the concepts is obtained from a detailed discussion of rotation-vibration spectra of diatomic molecules with only one vibrational degree of freedom. This includes approximate and exact separation of rotation and vibration, effective spectroscopic constants, the effects of nuclear spin and statistics, and transition probabilities derived from the form of the electric dipole moment function. The underlying assumptions and accuracy of the determination of molecular structure from spectra are discussed. Polyatomic molecules show many interacting vibrational degrees of freedom. Energy levels and spectra are discussed on the basis of normal coordinates and effective Hamiltonians of interacting levels in Fermi resonance, and in more complex resonance polyads arising from anharmonic potential functions. The resulting time-dependent dynamics of intramolecular energy flow is introduced as well. Effective Hamiltonians for interacting rotation-vibration levels are derived and applied to the practical treatment of complex spectra. Currently available computer programs aiding assignment and analysis are outlined.

High‐Resolution Fourier Transform Infrared Spectroscopy

Albert

Qüack

2011

Recent developments and applications of high‐resolution Fourier transform spectroscopy are reviewed. A short historical summary of the development of high‐resolution interferometric Fourier transform infrared (FTIR) spectrometers is given and the possibilities of the currently most highly resolving FTIR spectrometers, including a current prototype built for the Zürich group at the Swiss Light Source SLS as a synchrotron light source, are discussed. A short description of the principles of FTIR spectroscopy is given and the resolution of current spectrometers is illustrated by FTIR spectra of CO, CO 2 OCS, N 2 O, CS 2 , and CH 4 and its isotopomers. The computational tools necessary to analyze FTIR spectra are described briefly. As examples of rovibrational analysis of more complex spectra, selected molecules CHCl 2 F, CDBrClF, pyridine (C 6 H 5 N) and pyrimidine (C 4 H 4 N 2 ), and naphthalene (C 10 H 8 ) are discussed. The spectrum of CHCl 2 F, a fluorochlorocarbon, is of interest for a better understanding of the chemistry of the Earth's atmosphere. It also possesses an isotopically chiral isotopomer CH 35 Cl 37 ClF analyzed in natural abundance. CDBrClF is a chiral molecule and therefore the analysis of its rovibrational spectra provides the basis for carrying out further experiments toward the detection of molecular parity violation. The analyses of the pyridine, pyrimidine, and naphthalene FTIR spectra illustrate the potential of the new generation of FTIR spectrometers in the study of spectra and rovibrational dynamics of aromatic systems and molecules of potential biological interest. In particular, naphthalene is a prototype molecule useful in gaining an understanding of the unidentified infrared bands (UIBs) detected in several interstellar objects.