Experiment 5 Vibronic Spectrum of Iodine by UVVis
Absorption
Author:
Brent G. Klapthor
Group 6
Section 4, Tues 11:00 AM  2:00 PM
Partner: Jacob Waters
2/22/2011
Abstract:
The primary objective of this experiment was to use UVvisible light
spectroscopy to investigate the molecular structure of the diatomic iodine molecule.
This
first involved calculating the relative energies of Iodine in the ground state and excited
states.
An absorption spectrum for Iodine was generated through spectroscopy. The
difference in vibrational energies could then be plotted against the v’+1 labeled peaks in a
BirgeSponer plot. The intercept of this plot corresponded to the harmonic frequency, ω
e
,
found to be 138.253 cm
1
. The slope was used to calculate the first anharmonicity
parameter, ω
e
x
e,
to be 1.052 cm
1
.
Using equations and correlations discussed the
dissociation energy, D
e
was calculated to be 4611 cm
1
and the Morse parameter, β, to be
1.974 Å.
A Morse potential energy graph was constructed, illustrating the relative energy
levels of interatomic separations.
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Experiment 5 Vibronic Spectrum of Iodine by UVVis Absorption
I. Introduction
UVvisible light spectroscopy is a method commonly used to investigate the
quantum mechanics and atomic structure of elements. In this experiment, one of our
goals was to determine the vibrational energy of atomic iodine as internuclear spacing
varies. In doing so we were able to identify the equilibrium interatomic radius of iodine,
the state the molecule is most commonly found in. In other words, this is the spacing
which maximizes entropy, minimizes energy, and thus occurs most frequently in nature.
From the raw spectroscopy data, our first task was to generate a BirgeSponer
plot. By graphing the difference between successive vibrational energy states, ΔG
v
,
against (v +1), a line of the form
=

( + )
∆Gv
ωe 2ωexe v 1
was produced where ω
e
indicates the harmonic frequency and ω
e
x
e
is the first
anharmonicity parameter which can be found from the intercept and slope of the line
respectively.
Next, in calculation of the Morse potential, the group had to complete several
intermediate calculations such as the dissociation energy, D
e
, and Morse parameter, β.
The Morse parameter equals,
=
β
8π2cμωexeh
where in addition to the variables mentioned above are the constants the speed of light, c,
Planck’s constant, h, and the reduced mass, μ.
The group used spectroscopy to create calculations for the Vibronic energy levels
at a range of interatomic spacing of each iodine molecule.
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 Spring '11
 James
 Chemistry, Atom, uvvis absorption, vibronic spectrum

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