1. Tokyo Institute of Technology Hiroyuki Kawasaki, Asao Mizoguchi, Hideto Kanamori High Resolution Infrared Spectroscopy of CH 3 F-(ortho-H 2 ) n cluster in solid para-H 2 ISMS RJ06

2. para-H 2 ortho-H 2 n = 0 n = 1 The image of CH 3 F-(ortho-H 2 ) n... Introduction Spectra of ν 3 of CH 3 F-(ortho-H 2 ) n by FTIR Previous research c CH 3 F-(o-H 2 ) n in solid p-H 2 by using FTIR* *Yoshioka and Anderson JCP, 119, 4731 (2003)

3. para-H 2 ortho-H 2 n = 0 n = 1 The image of CH 3 F-(ortho-H 2 ) n... Introduction Spectra of ν 3 of CH 3 F-(ortho-H 2 ) n by FTIR Previous research c CH 3 F-(o-H 2 ) n in solid p-H 2 by using FTIR* *Yoshioka and Anderson JCP, 119, 4731 (2003) By using cw-Quantum Cascade laser in our Lab.** **JMS, 310, 39 (2015)

4. Spectrum of CH 3 F-(ortho-H 2 ) n Introduction Time dependence of Integrated Intensity The time behavior of n = 3 is different from others → Is it a magic number ? “3” is key number of D 3h (hcp) and C 3v (CH 3 F) Previous research CH 3 F-(o-H 2 ) n in solid p-H 2 by using FTIR* *Yoshioka and Anderson JCP, 119, 4731 (2003) By using cw-Quantum Cascade laser in our Lab.** **JMS, 310, 39 (2015)

5. Means Polarization spectroscopy of the CH 3 F / p-H 2 system Purpose To determine the alignment of CH 3 F in solid p-H 2 ν 3 band (C-F stretching) is a parallel band → Only the parallel component of laser beam to the C 3 axis is absorbed * Y. P. Lee et al., JCP, 129, 104502 (2008) CH 3 F can rotate only about its symmetry axis* Is C 3 axis along c-axis of solid p-H 2 ? para-H 2 ortho-H 2 The C 3 axis is locked in a particular direction c

6. The experimental setup Detector Oscilloscope Function Generator Mirror Etalon Attenuator 45° c rotary pump lq N 2 lq He Mirror Detector GP(45˚) Hamamatsu QCL V GP(|| or ⊥ ) Cryostat c-axis || (Parallel) (Perpendicular) ⊥ 45˚ Substrate (2 K) Definition of ⊥ / || for the probing laser ⊥ || Sample gas 1.8 K CH 3 F: 0.4 ppm o-H 2 : 100 ppm

7. Ratio of ⊥ / || ⊥ / || 45˚ No.1 45˚ No.2 ⊥ || Experimental result / incident angle 45˚ Typical spectra of // and ⊥ Ratio of ⊥ / || = 1.45(19) ← No relation with number of o-H 2 If the C 3 axis is locked firmly in the c-axis of solid p-H 2 ⇒ ⊥ should be not observed → ⊥ / || = 0 If the alignment of CH 3 F is completely random in solid p-H 2 ⇒ The intensities of ⊥ and || are equal → ⊥ / || = 1 The C 3 axis is not locked in the c-axis of solid p-H 2

8. The setup configuration The measurement setup 2 Changing the incident angle If CH 3 F has random orientation around the c-axis of solid p-H 2 → ⊥ / || = 1 c-axis ~ 0˚ Substrate (2 K) c-axis 45˚ Substrate (2 K) || ⊥ ⊥ To check the incident angle dependence of ⊥ / ||

9. Experimental result / incident angle 0˚ comparison of the ⊥ / || values between 45˚ and 0˚ ⇒ Clearly different Ratio of ⊥ / || = 0.97(5) The C 3 axis is randomly oriented around c-axis of solid p-H 2, but it is limited the angle to the c-axis Polarization dependence of peak intensity Incident angle dependence ⊥ / || 0˚ 45˚ Polarization dependence of peak intensities n = 0 and 1 ⇒ Almost same value

10. Model for calculation θ dependence of ⊥ / || z = c-axis θ φ φ : 0 – 360° Cal. result of θ dependence ⊥ / || ← C 3 axis of CH 3 F Cal. at incident angle45˚ Calculation ⊥ / || ∝ μ ・ E ⊥ / μ ・ E || ⇒ integrated about φ (0 - 360˚) From the Exp. at 0˚ incident angle The C 3 axis is randomly oriented around c-axis of solid p-H 2

11. Calculation ⊥ / || ∝ μ ・ E ⊥ / μ ・ E || The C 3 axis would be more stable when it is perpendicular to the c-axis θ φ φ : 0 – 360° Cal. result of θ dependence and Exp. result ⇒ integrated about φ (0 - 360˚) 65˚ ≲ θ ≲ 115˚ ⊥ / || Exp. at 45˚ From the Exp. at 0˚ incident angle C 3 axis of CH 3 F θ dependence of ⊥ / || 1.45(19) z = c-axis Model for calculation ← Cal. at incident angle45˚ Corresponding angle Corresponding θ angle The C 3 axis is randomly oriented around c-axis of solid p-H 2

12. Discussion Cal. of θ dependence and Exp. Model 1 Model 2 Model 1 The C 3 axis of CH 3 F is in the in-plane of hcp Model 2 The C 3 axis points to the center of gravity of a triangle plane of the nearest sites C 3 symmetry on the C 3 axis ⊥ / || = 1.45(19) at Exp. ⊥ / || 1.411.33

13. Summary Observation of the polarization dependence of CH 3 F Proposing the models for the CH 3 F alignment Polarization spectroscopy of CH 3 F in solid para-H 2 At incident angle 45˚ → ⊥ / || = 1.45(19) At incident angle 0˚ → ⊥ / || = 0.97(5) Determination of the alignment → 65˚ ≲ θ ≲ 115˚ The C 3 axis of CH 3 F would be more stable when it is perpendicular to the c-axis of solid p-H 2

15. The anisotropic field potential would be able to make the CH 3 F direction There is the possibility that C 3 axis of CH 3 F on the in-plane is more stable Past research Fig. Image of IP and OP Katsuki, Nakamura, Momose, JCP, 116, 20 (2002) Support documentation : anisotropic filed potential The crystal field parameters are different between in-plane and out-of-plane pair of p-H 2 and o-H 2

16. The change of each peak n = 0 increases n = 1 and n = 2 decrease n = 3 increases Time dependence of Integrated Intensity By nuclear spin conversion The conversion time on n = 3 would be slow Time dependence of population The population of sum of n = 0 ~ 2 was almost constant The three levels can be considered closed Support documentation : Population change

17. Time dependence of each peak Each peak changes the intensity with the passage of time o-H 2 at low temperature change to p-H 2 with the passage of time Wavenumber (cm -1 ) 23 hours 18 hours 12 hours 6 hours 0 hour n = 2n = 1n = 0n = 3 Support documentation :Time dependence

18. para-H 2 ortho-H 2 Image of the change due to migration by pumping Image of the change due to nuclear spin conversion Pump The number of ortho-H 2 dose not change para-H 2 ortho-H 2 Time The site of ortho-H 2 migrates to the next or more far site The number of ortho-H 2 changes The ortho-H 2 is converted to para-H 2 through an interaction with CH 3 F in low temperature n = 1 n = 0 n = 1 n = 0 Support documentation :Time dependence

19. x z = c-axis θ ≈ 70.5° Hypothesis patterns to the direction of CH 3 F in solid p-H 2 Calculation result CH 3 F axis direction θ should be in ~ 65˚ < θ < ~ 115˚ 1. x z = c-axis 2. 3. Support documentation : Models x z = c-axis

20. Support documentation : QCL http://www.ohno.riec.tohoku.ac.jp/japanese/overview-file/8.htm transition between subbands electron Laser transition between bands electron hole Laser Semiconductor Laser ・ Since it uses the transition between bands, the wavelength of this laser beam depends on the materials Quantum Cascade Laser ・ Since it uses the transition between subbands, the wavelength of this laser beam can change with changing the width of semiconductor superlattices ・ Getting high power by superlattices

21. 数距離 （Å） First nearest neighbor 123.78 Second nearest neighbor 65.35 Third nearest neighbor 26.17 Fourth nearest neighbor 186.56 J. Chem. Phys. 119, 4731 (2003) Support documentation : V dip-quad

22. Support documentation : p-H 2 &o-H 2 para-H 2 ortho-H 2 H H H H I = 0, J = 0, 2, 4, ・・・ I = 1, J = 1, 3, 5, ・・・ 存在比 31 エネルギー Energy (meV) J = 3 J = 1 J = 0 J = 2 45.24 meV 90.48 meV 15.08 meV

23. Support documentation : o- &p-CH 3 F E rot = (A-B)K 2 + BJ(J+1) A = ~ 5 cm -1, B = ~ 0.8 cm -1 K = 0 (ortho-CH 3 F) : I = 3/2 K = 1 (para-CH 3 F) : I = 1/2 (J, K) = (0, 0) → 1 メチル基由来 回転エネルギー ボルツマン分布から考えた 2 K における分布数 (J, K) = (1, 1) → e -6 (J, K) = (2, 2) → e -12