1. Lineshape analysis of CH3F-(ortho-H2)n absorption spectra in 3000 cm-1 region in solid para-H2
Yuki Miyamoto
Graduate School of Natural Science and Technology, Okayama University, JAPAN
Takamasa Momose
Department of Chemistry, The University of British Columbia, CANADA
and
Hideto Kanamori
Department of Physics, Tokyo Institute of Technology, JAPAN
67th International Conference on Molecular Spectroscopy, The Ohio State University, USA, June 18 – 22, 2012

2. CH3F in solid para-H2
K. Yoshioka and D. T. Anderson J. Chem. Phys (2003) etc…
ortho
Low
Regular series of lines due to CH3F-(ortho-H2)n in the ν3 and 2ν3 band
High
Y.-P. Lee, Y. –J. Wu and J. T. Hougen J. Chem. Phys (2008)
Assignment of other transitions with axial rotation structure
ν1, 4
ν2, 5 ν6
in Ar
in pH2

3. Question Only in the ν3 band ?
Ans.; Other bands also consist of cluster components. (previous talk)
In this talk, FTIR results will be presented.

4. FTIR Spectra in 3μm The 2859 band ? Three bands were observed.ν1
* in this talk, discussion will be focused on these three band and the ν3 band
According to Lee et al….
3010 cm-1 = ν4
2962 cm-1 = ν1
The 2859 band ?
From gas phase experiments,
2859 cm-1 = 2ν5 strongly mixed with the ν1 via Fermi resonance

5. ortho-H2 Dependence
2ν5 ν1
250 ppm
3900 ppm
5500 ppm
res. 0.1 ~ cm-1
Asymmetric lines of other bands show lineshift and broadening

6. Fitting Analysis
If lineshift and broadening is attributed to CH3F-(ortho-H2)n,
these broaden lines can be decomposed into each component using shape of the ν3 band
Parameters determined from the ν3 band
An(X); normalized intensity of n-th component at [ortho-H2] = X
Δωn; frequency difference of n-th component from the n = 0 component
Δωn
n=0
An(X)
An(X); common for all bands
Δωn; scaled for each band

7. Superposition of normalized Lorentzian
scale of lineshift
relative intensity
freq. of n = 0
linewidth

8. Observed lineshape were represented well.ν1
2ν5
250 ppm
5500 ppm
3900 ppm
Observed lineshape were represented well.

9. Fitted Parameters freq. of n = 0 lineshift linewidth
relative intensity
lineshift
linewidth
kth-band
Sym.
Gasa
[cm-1] Xb
[ppm]
　ν0c
Matrix shift
　α(k)(X) d
　β(k) (X) e
　γ(k) (X) f n3 a1
250
1040.2
(0.0003)
-8.41 1
---
0.017
(0.0006)
3900
(0.0005)
0.045
(0.0015)
5500
(0.0048)
0.155
(0.0142)
2859 cm-1
(2n5)
2859.7
(0.0032)
-3.54
0.13
(0.00)
-0.17
(0.016)
0.163
(0.0100)
2859.8
(0.104)
-3.44
0.15
(0.01)
(0.039)
0.459
(0.0980)
(0.35)
0.16
(0.02)
-0.24
(0.107)
0.488
(0.2670)
2962 cm-1
(n1)
2962.7
(0.0057)
-3.55
0.23
-0.16
(0.031)
0.328
(0.0215)
2962.8
(0.0945)
-3.45
0.25
-0.19
(0.036)
0.521
(0.0972)
2962.4
(0.165)
-3.85
0.27
-0.36
(0.049)
0.446
(0.1570) n4 e
3009.8
(0.0113)
-0.96
0.26
-0.84
(0.063)
0.784
(0.0436)
(0.351)
0.28
-0.54
(0.131)
1.258
(0.5540)
3009.4
(0.268)
-1.36
0.30
-0.79
(0.080)
0.825
(0.2840)

10. Comparison with Laser Spectrum
2ν5
0.12cm-1
0.12cm-1
Good agreement !

11. Lineshift and Linewidth
2ν5 ν1 ν1
2ν5
Shift of CH3F-(ortho-H2)n
ν3 ; Red shift for larger n
ν4; Blue shift for larger n
ν1,2ν5 ; shift is small
Broader at higher ortho concentration
The ν1 and 2ν5 are mixed via Fermi resonance similar character
Different behaviors among these bands should be due to the structure and dynamics of clusters.

12. Mixing between ν1 and 2ν5
Mixing of vibrational modes via Fermi resonance
( k = 1, 2)
Transition intensity of |k>
Mixing coefficient can be estimate from intensity ratio between ν1 and 2ν5
our experiment ; I[ν1]: I[2ν5] = 1:0.6
in gas phase; I[ν1]: I[2ν5] = 1:0.9
J. P. Champion et al.
J. Mol. Spectrosc. 96, 422 (1982)
semiquantitative agreement
Mixing ratio is same order in solid para-H2

13. Summary
Vibrational absorption transitions of CH3F and its cluster with ortho-H2 in solid para-H2 were studied by FTIR absorption spectroscopy.
Three bands at 3 μm region were observed as structure less asymmetric broader peaks.
By using the cluster model fitting, these bands were resolved into each cluster component.
Mixing ratio of the ν1 and 2ν5mode with Fermi resonance was derived from the observed intensity ratio, and it agreed with the analysis of the gas phase spectra.