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QUANTUM ROTATIONS IN METHYL IODIDE: A Study Using HFBS and FANS

This study investigates the rotational dynamics of CH3I using high-resolution techniques, specifically the High Flux Backscattering Spectrometer (HFBS) and the Filter Analyzer Neutron Spectrometer (FANS). The HFBS provided critical data at low temperatures, revealing tunneling energies, barrier heights, and transition energy for the libration dynamics of methyl iodide. Additionally, FANS data helped to validate these findings. With resolutions measuring vibrational motions from approximately 1 μeV to 1 meV, this research enhances our understanding of quantum rotations in complex molecular systems.

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QUANTUM ROTATIONS IN METHYL IODIDE: A Study Using HFBS and FANS

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  1. QUANTUM ROTATIONS IN METHYL IODIDE: A Study Using HFBS and FANS Group C Christopher Kitchens Yifu Ding Amit Kumar Joon Ho Roh

  2. High Flux Backscattering Spectrometer

  3. High Flux Backscattering Spectrometer • resolution ~ 1 μeV • energy transfers upto ±50 μeV • motions on ns timescales • momentum transfers from 0.25 Å-1 to 1.75 Å-1

  4. BULK CH3I DYNAMICS Inelastic Quasielastic CH3I melting point = 206 K Use 3-fold symmetric potential

  5. HFBS DATA FOR CH3I at T = 8 K V3 = 42 meV Et = 2.3 μeV E ~ 7.5 meV ? Check with FANS

  6. Filter Analyzer Neutron Spectrometer • measures vibrational motion • energy transfers of order 10 to 100 meV • resolution about 1 meV

  7. FANS DATA at T = 12 K Fit Results : Elib = 13.2 meV

  8. HFBS DATA FOR CH3I at T = 40 K

  9. EISF Fitting for T = 40 K data Rfit = 0.965 Å Rexp = 1.03 Å

  10. SUMMARY • HFBS was used to study the rotational dynamics of CH3I. • Tunneling energy was determined using HFBS from which the barrier height and the transition energy for libration was calculated. • Data from FANS was used to verify the prediction of the libration transition energy. • Radius of the methyl group was estimated by fitting the EISF data.

  11. ACKNOWLEDGEMENTS • To NIST and NSF for the opportunity to experiment and study Neutron Spectroscopy and its applications • To the NCNR Summer School Coordinators and Instructors for their assistance and guidance

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