1. Precision Laser Spectroscopy of H 3 + Hsuan-Chen Chen 1, Jin-Long Peng 2, Takayoshi Amano 3,4, Jow-Tsong Shy 1,5 1 Institute of Photonics Technologies, National Tsing Hua University, Taiwan 2 Center for Measurement Standards, Industrial Technology Research Institute, Taiwan 3 Department of Physics and Astronomy, University of Waterloo, Canada 4 Department of Chemistry, University of Waterloo, Canada 5 Department of Physics, National Tsing Hua University, Taiwan 68 th International Symposium on Molecular Spectroscopy 117/06/2013

2. Background  Reported the first observation of the Lamb-dip of the R(1,0) line of the 2 band of H 3 + Phys. Rev. Lett., 109, 263002(2012) 81720371.550(250) MHz  In this work, Extended the measurements to several more vibration-rotation transitions Transition frequencies and the pressure broadening coefficients. 217/06/2013

3. Why is it so important to achieve high- precision measurements of lines of H 3 + ?  The most important interstellar molecule First laboratory identification ( Oka, 1980 ) First detection in interstellar clouds ( Geballe and Oka, 1996 )  A benchmark molecule for highly sophisticated ab initio calculations. Predictions of accurate vibration rotation energies in particular for high v and J states  Potential energy surface with non-adiabatic and relativistic corrections. 317/06/2013

4. Outline of the experimental setup 417/06/2013 Optical Parametric Oscillator 1)Singly-resonant OPO 2)5 % mol. Doped MgO: PPLN 3)Mode-Hop-Free Tuning: > 0.5 THz 4)Output Power: 130 mW @3.41  m 5)Stability: 500 MHz @ 8 hours Discharge Tube 1)Extended Negative Glow Discharge 2)Discharge Current:  17 mA 3)Magnetic Field:  200 Gauss Optical Frequency Comb (OFC) 1)All Fiber-based Component 2)Repetition Rate: 250 MHz 3)GPS-referenced Rubidium Clock 4)Supercontinuum: 1  2.2  m

5. Singly Resonant OPO Idler Wavelength :2.7 – 3.9 μm Average Power : > 300 mW Frequency Tuning : > 40 GHz (Mode-Hop-Free) Free-Running Stability : < 500 MHz @ 8 hours 17/06/20135

6. Fiber Optical Frequency Comb  Repetition Rate : 250 MHz  Supercontiuum : 1030 ~ 2200 nm  RF Reference : GPS-locked rubidium clock  Accuracy : < 10 -12 @ 1000 sec (  a few kHz in the MIR region) 1.062 μm 1.4-1.8 μm2.7-3.9 μm Frequency determination 1.Lock signal to comb, 2.Lock pump to line center, and 3.Measure pump frequency 17/06/20136

7. Determination of OPO Frequencies 7 Roughly estimated by wavelength meter Readings of frequency synthesizer Frequency counters 17/06/2013

8. 3 rd Derivative Signal of Saturation Dip 817/06/2013 H 3 + 2 fundamental band R(1,0)R(3,0)

9. Confirmation of the frequency measurement CH 4 F 2 (2) P(7) transition of the ν 3 band 88376181.633(11) MHz This work 88376181.6005(20) MHz CIPM recommended value 17/06/20139

10. Measured Frequencies for H 3 + 1017/06/2013 K. –Y. Wu, PhD Thesis, National Tsing Hua University (2008) A. R. W. McKellar and J. K. G. Watson, J. Mol. Spectrosc. 191, 215 (1998)

11. Homogeneous Linewidth Investigation of H 3 + 1117/06/2013 Homogeneous linewidth measured at 60 mTorr of H 2 pressure and with IR power of 100 mW. Corrections for the power broadening should be made.

12. Pressure Broadening Coefficient 1217/06/2013 R(3,0) Transition

13. Pressure Broadening Coefficient  Elastic collisions  Non-reactive collisions  Reactive collisions  Langevin rate represents only a part of it. 17/06/201313 Experimental Value: 28.0 ± 2.8 MHz/Torr for R(3,0) Calculated Value: 9.8 MHz/Torr (Assumed translational temperature to be 300K) More measurements should be done to obtain the J and K dependence.

14. Conclusion  Accurate frequencies for the 2 vibration-rotation lines of H 3 + have been measured. The accuracy of frequency measurement can be as good as  250 kHz.  We determined the pressure broadening parameters from the linewidth investigation and compared the results with the calculated value from Langevin model. 1417/06/2013

15. Acknowledgments National Science Council and the ministry of Education of Taiwan NSERC ( Natural Science and Engineering research Council of Canada ) University of Waterloo 17/06/201315

16. Thank you for your attention 1617/06/2013

17. 1717/06/2013