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Laser Induced Fluorescence in Iodine

This Immersion, designed to focus on the fundamentals of molecular spectroscopy, will introduce an affordable, straightforward and highly visual advanced laboratory experiment to study the internal structure of diatomic molecules. Participants will use various spectroscopic techniques to scrutinize the vibrational and rotational spectra by measuring the vibrational and rotational energy spacing of the gas phase diatomic molecules. Additionally, during each session time will be devoted to discussing the theory underpinning the experiments.

The Immersion will include two simple experiments. First, electron-impact excitation using a nitrogen discharge tube (Am. J. Phys., Vol. 80, 664-669, August 2012) will prepare the foundation for the second experiment which is based on the laser induced fluorescence using molecular iodine in the gas phase. Participants will scrutinize the spectra about the potentials associated with vibrational states of the diatomic molecules and assign spectral lines based on the transition probability, build vibrational energy level diagram and tabulate Deslandres tables, evaluate harmonic and anharmonic characteristics of the states and thereof the merits of the harmonic approximation for the molecular oscillator. From the measurements participants will extract the molecular constants such as dissociation energies of the molecular potential, depth of the potential well and the effective force constant of the molecular bond. In the second part of the Immersion, participants will study the rotational structure of the nitrogen molecular ion and molecular iodine. Vibrational and rotational temperatures, commonly used in statistical thermodynamics, will be extracted. These measurements are important in combustion diagnosis, gas-phase chemistry, plasmas, and atmospheric physics. By the end of the Immersion, each participant will have the course materials and hands-on experience necessary to create a similar instructional lab at his or her own institution.