The Iodine Spectrum©
George Long
Department of Chemistry
Indiana University of Pennsylvania
Indiana, PA 15705
United States

Theresa Julia Zielinski
Department of Chemistry, Medical Technology, and Physics
Monmouth University
West Long Branch, NJ 07764-1898
United States
mail to: tzielins@monmouth.edu

The goal of this document is to present a systematic development of the relationship between spectroscopic experiments and the determination of molecular bond lengths in the excited state of diatomic molecules for which a high resolution vibronic spectrum is available. This document can serve as a template for students to use for data analysis of the UV-Vis spectrum of I2 or other diatomic gases. Use of this document as a template requires student UV-Vis spectral data acquired in the laboratory. Faculty can also use this document with the enclosed sample data for student practice when an instrument is unavailable. The details of the Birge-Sponer plot are clearly illustrated. The document discusses the Morse potential and includes calculations with this potential function using correct units. Students can see clearly the mathematical steps leading to the calculation of the equilibrium bond length of the excited state of iodine. The Morse potential for both the ground state and excited state permit discussion of the effect of excitation on molecular geometry. This document represents a way to make data analysis and work with the concepts for this experiment more efficient for students. Student exercises are fully integrated into the presentation and implementation of the mathematical concepts of this topic. References for the laboratory experiment are included.

This document is one of a suite of documents treating the vibronic spectra of molecules. The other documents in the set are: MorsePotential, Introduction to Franck-Condon Factors, and Vibronic Spectra of Diatomic Molecules and the Birge-Sponer Extrapolation. When used together these documents form a powerful integrated collection of concept builders for students studying spectroscopy in a Junior or Senior college level quantum chemistry course. References for the experiment are included in the document.
Editor's Commentary
Audiences: Upper-Division Undergraduate
Pedagogies: Computer-Based Learning
Domains: Physical Chemistry
Topics: Mathematics / Symbolic Mathematics, Quantum Chemistry, UV-Vis Spectroscopy, Spectroscopy
Elements: Iodine
File NameDescriptionSoftware TypeSoftware Version
IodineSpectrum.mcd JCE Mathcad Computational Document Mathcad
IodineSpectrum.pdf Read-Only Document
I2spectrum.mw JCE Maple V
I2spectrum-mw.pdf Computational Document
JCE JCE Subscribers only: name and password or institutional IP number access required.
Long, G.; Zielinski, T. J. J. Chem. Educ. 1998 75 1192.
Comments to: George Long at grlong@grove.iup.edu and Theresa Julia Zielinski at tzielins@monmouth.edu
©Copyright 1998 Journal of Chemical Education