Quantum Rotational Dynamics of CH3I

Group D

Y Liu, S Jonas, V Atakan, H Wu, S Omar-Diallo, I-K. JeongD. Phelan

System description

tunneling

libration

stochasticreorientation

kBT

Methyl Iodide Three fold potential model

V3

θ3cos12

VθV 3

Numerical Values of Energy Level

Experimental Goals

What we are looking for:1. The “height”of the V3 well

2. The librational energy

3. The projected radius of Hydrogen from Carbon

Why HFBS and FANS?

The tunneling energy is quite small Tunneling process have energies on order of ~

eV

The HFBS has high resolution. ~1 eV, well below the conventional triple-axis and neutron

TOF spectrometers.

The FANS has high energy transfer (~100meV)

HFBS and FANS diagram:

How HFBS works

The HFBS varies incident energy by using a cam-based Doppler-driven monochromator.

Phase Space Transformer increase flux

4x. Very large analyzer array, 20% of 4The scattering chamber is operated under vacuum instead of Ar or He improving the signal-to-

background ratio.

Tunneling Energy: ~2.3eV V3 ~ 42meV

Inelastic Scattering (T = 8K)

Rexp =1.03A

Rcal =1.027A

Elastic and Quasielastic Peak EISF Fitting

Quasielastic Analysis (T = 38K)

Jump Diffusion Model:

))3(21(3

10 Qrj

))3(21(3

10 Qrj

Librational Energy Study by FANS

1st libration energy: ~14meV

Acknowledgement

NIST

Zema Chowdhuri, Robert Dimeo (HFBS)

Craig Brown (FANS)

Members of Group D, summer school 2003