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

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, (2012) (250) MHz  In this work, Extended the measurements to several more vibration-rotation transitions Transition frequencies and the pressure broadening coefficients. 217/06/2013

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

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  m 5)Stability: 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

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

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

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

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

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

Measured Frequencies for H /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)

Homogeneous Linewidth Investigation of H /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.

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

Pressure Broadening Coefficient  Elastic collisions  Non-reactive collisions  Reactive collisions  Langevin rate represents only a part of it. 17/06/ 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.

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

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

Thank you for your attention 1617/06/2013

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