1. Rotation about a-Axis CH3F in Solid p-H2 Nuclear Spin Conversion
Yuan-Pern Lee1, 2 Yu-Jong Wu1 and Jon T. Hougen3
 1Department of Applied Chemistry, National Chiao Tung
University, 1001 Ta-Hsueh Road, Hsinchu 30010, Taiwan.
2Institute of Atomic and Molecular Sciences,
Academia Sinica, Taipei 10617, Taiwan.
3Optical Technology Division, NIST,
Gaithersburg, MD , USA.

2. Motivation = General Question:
Can Large-Amplitude Motions (LAMs)
be usefully studied in solid p-H2?
Definition of LAMs (|r|  rbond).
Examples:
Rotation about a,b,c principal axes
Internal rotation of CH3 group
Inversion of NH3 or NH2 group
4. Conformational changes

3. Rotation possibilities for CH3F in p-H2
Rotation about a,b,c axes
3 angles, |JKM
2. No rotation at all
3 Librations |u1,u2,u3
3. Rotation about a-axis only?
|u1,u2 |K
CH4, C2H4, CO are case #1 in p-H2

4. Rotation-Vibration energies in p-H2
Rotational quantum numbers
J,M  u1,u2 (librations). K = 0,1,2,..
Vibrational angular momentum:
l=0 for A vibrations (nondegenerate)
l=1 for E vibrations (degenerate)
E = o + AK2 –2AKl

5. Group theory for CH3F in p-H2 C3v  E, C3, C32, 3v
 C3  E, (123), (123)2
Symmetry species A and E (separable)
Vibrations: vA (1,2,3) or vE (4,5,6)
Rotations: rA (K=0,3) or rE (K=1,2).
Rovibrational: vrA (K l = 0,3) IH = 3/2
vrE (K l = 1,2) IH = 1/2

6. For visualization: Keep only J = K levels
Use gas-phase notation (bad): KJ(J,K)

7. Expect 1 parallel “line” in p-H2:
QQ(0,0) = 0
QQ(1,1) = 0 + A A 0
Expect 3 perpendicular lines in p-H2:
RR(1,1) = 0 + 4A – 4AKl  A
RR(0,0) = 0 + A  2AKl
PP(1,1) =   A

8. Ar H2

9. Temperature
Variation
Studies
Intensities
Normalized
To Central
Peak

10. Nuclear Spin Conversion Rate

11. Future work:
1. a-axis rotation of other symmetric tops:
CH3-CCH, CH3-Cl, CH2=C=CH2
Next talk: Miyamoto and Momose
CH2Cl in p-H2
2. Other types of large-amplitude motion

12. First study was on internal rotation
in CH3OH in solid p-H2
Spectra of five fundamental bands were
interpreted as showing no overall rotation,
but A-E internal rotation splittings similar
to those for the same bands in the gas.
What is internal rotation motion in p-H2?
-OH only? -CH3 only? Both?