2015 BFY II Abstract Detail Page
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||An Experiment Revealing some Characteristics of Diatomic Molecules by Spectral Analysis of Laser Induced Fluorescence of Iodine
||The emission spectrum from the laser-induced ?uorescence (LIF) of iodine can be used to demonstrate the vibrational energy structure of homonuclear diatomic molecules at room temperature. Iodine is an especially suited molecule for LIF measurements because it absorbs about 20,000 lines in the 490- to 650-nm visible region of the spectrum and displays discrete vibrational bands at moderate resolution. Although the experimental setup is remarkably simple, the spectral analysis provides an excellent exercise of applied quantum mechanics. The apparatus consists of a 532-nm diode laser, an iodine cell, and a handheld spectrometer which delivers the LIF spectrum associated with the vibrational states of the diatomic molecules. The students are expected to assign spectral lines based on the transition probability between vibrational levels, build a vibrational energy level diagram and tabulate a Deslandres table. Subsequently, they process these data by a procedure called Birge-Sponer treatment to estimate the harmonic and anharmonic characteristics of the two vibronic states involved in the radiative transitions and model the energy profile of the vibrator. Based on these and on a Morse-potential model, they can calculate a set of molecular constants, such as the dissociation energies of the molecular potential, the inter-atomic separation and force constant of the molecular vibrator, as well as the width-parameter of the Morse potential. All these ingredients allow the students to plot the potential of the excited state and discuss the merits of the model for the quantum mechanical oscillator.
Morrisville State College
Morrisville, NY 13408
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