1. Chuanxi Duan (段传喜） Central China Normal University Wuhan, China
71th Meeting - June 20-24, 2016
Champaign-Urbana, Illinois
Vibration-rotation-tunneling spectrum of formic acid dimer in the 7.3 μm region
Chuanxi Duan (段传喜）
Central China Normal University
Wuhan, China

2. Outline Previous high resolution studies Experimental method
Results and analysis
HCOOH-HCOOH
HCOOD-HCOOH
HCOOD-HCOOD
Conclusions

3. Formic acid dimer: a prototype for double hydrogen-bond and proton transfer
Key questions:
Mode-specific tunneling splitting
The isotope effect
J. Chem. Phys. 117, 7162 (2002)

4. Previous high resolution studies on formic acid dimer
Özgür Birer and Martina Havenith, Annu. Rev. Phys. Chem. 60, 263 (2009)

5. The Fermi-triad system of (HCOOH)2 in the C-O stretching region, lead-salt laser diodes
J. Chem. Phys. 140, (2014)
ISMS 2014, RD07

6. Can we find a less-perturbed IR band for (HCOOH)2 ?

7. Experimental setup DFB-QCL Astigmatic multi-pass cell to pump IR
Laser
controller IR P
Nozzle
Valve
Reference gas cell
NI-DAQ
Detector
ulse
generator
Etalon
Gas supply
Wavemeter
Experimental setup
DFB-QCL
Astigmatic multi-pass cell

8. Multi-step Rapid-scan with DFB-QCL
Successively moving pulsed jet
~1.5 ms
Reference
gas
Passive frequency locking
Merged jet spectrum
10 × 1.0 ms

9. Supersonic jet: HCOOH/ Ar, DFB-QCL
HCOOH-HCOOH, C-H bending fundamental
Observed
Simulated

10. HCOOH-HCOOH observed simulated
Close to the band origin: observed and simulated spectrum are in good agreement.

11. HCOOH-HCOOH
observed
simulated
by PGOPHER

12. Energy crossing between two tunneling components: J ~ 12.5
Ground state, Ka = 0
Energy crossing between two tunneling components: J ~ 12.5

13. Ground vibrational state, Ka = 1
Energy crossing between two tunneling components:
J ~ 12.5, 13.5

14. Excited vibrational state, Ka = 0
Energy crossing between two tunneling components:
J ~ 17.5

15. Rotation-tunneling coupling (c-type Coriolis interaction)
Observed
Simulated
Fit and simulated by PGOPHER

16. HCOOH/D2O mixtures, Ar buffer gas
DFB-QCL

17. H-O-C-H bending fundamental
HCOOH-HCOOD
H-O-C-H bending fundamental H
Observed D
Simulated

18. D-O-C-H bending fundamental
HCOOD-HCOOD
D-O-C-H bending fundamental D
Observed D
Simulated

19. Observed linewiths (FWHM) for HCOOH-HCOOD, HCOOH and HCOOD-HCOOD

20. HCOOH-HCOOH
DCOOH-DCOOH
HCOOH-HCOOD
HCOOD-HCOOD
DCOOD-DCOOD
Ground state
0.0165(2)
0.0125(3)
<
<
< 0.002
C-O stretching
0.0115(3)
0.0031(3)
C-H bending
0.0045(1)
J. Chem. Phys. 140, (2014), and this work
Annu. Rev. Phys. Chem. 60, 263 (2009)

21. Conclusions
A multi-step rapid-scan method for pulsed jet IR spectroscopy based on DFB-QCL is developed.
The C-H bending fundamental bands are measured and analyzed for HCOOH-HCOOH, HCOOD-HCOOH, and HCOOD-HCOOD.
Strong rotation-tunneling coupling in HCOOH-HCOOH is identified.

22. Acknowledgement Wei LUO (left) Yuluan ZHANG (middle)
Zhuang LIU (right)
Prof. Fengqi LIU and Lijun WANG
Institute of Semiconductor
Chinese Academy of Sciences