Precision Measurement of the Ionization Energy of the GK 1 Σ + g (v = 1, N = 1) State of Molecular Hydrogen.

Transcription

1 Precision Measurement of the Ionization Energy of the GK 1 Σ + g (v = 1, N = 1) State of Molecular Hydrogen. Maximilian Beyer, Daniel Sprecher and Frédéric Merkt Laboratory of Physical Chemistry, ETH Zurich, Switzerland 68th International Symposium on Molecular Spectroscopy Ohio State University, June 17-21, 213 D. Sprecher, M. Beyer, and F. Merkt, Mol. Phys., in press. Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

2 Ionization Energy of Molecular Hydrogen: Step by Step Divide And Measure X low-n interval low-n high-n interval - efficient population of the low-n state - transition frequency accessible with Ti:Sa system high-n X + interval - least perturbed Rydberg series to facilitate highly accurate MQDT calculations X (v =, N=1) B (v =3, N=2) GK (v =1, N=1) 56p1 1 (S=, v + =) [1] S. Hannemann et al., Phys. Rev. A, 74, (26). [2] J. Liu et al., J. Chem. Phys. 13, (29). [3] D. Sprecher et al., Faraday Discuss. 15, 51 (211). X + n=56 n=5 n=4 n=3 n=2 X... Ionization continuum mmw spectroscopy and MQDT σ 1 khz [3] 396 nm 792 nm 792 nm σ = 8.7 MHz [2] GK (3dσ) EF (2sσ) 2 22 nm σ = 5.4 MHz [1] IP: σ 11.1 MHz [2] nm (a) (b) (c) 566 nm B (2pσ) 16 nm Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

3 Multichannel quantum defect theory (MQDT) treatment "Least perturbed" Rydberg series in o-h2 : np11 (S =, v + = ). I Use mmw-spectra to refine ab initio quantum defects [1]. I Prediction uncertainties for binding energies (54 64p11 ): 1 khz [2]. np,nf nd mmw 53d 56p UV 2 hyperfine splitting (MHz) I -2 2pB 25 khz VUV -4 1sX frequency (MHz) principal quantum number n 64 [1] A. Osterwalder et al., J. Chem. Phys. 121, 1181 (24). [2] D. Sprecher et al., Faraday Discuss. 15, 51 (211). Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

4 Experimental Setup 56pπ (v + =,N + =1) 3dσ GK (v=1,n=1) Ti:Sa laser (792 nm) probe gas (general valve) 2pσ B (v=3,n=2) VIS laser (566 nm) skimmer vacuum pump skimmer 1sσ X (v=,n=1) VUV laser (16 nm) pulse energies< 5 mj pulse width 2 ns bandwidth < 1 MHz VIS NIR VUV excitation region electrode stack AOM v Laser + 1 GHz Etalon FSR= MHz Glass fiber Ti:Sa dichroic mirror magnetic shielding vacuum pump HeNe-cw-laser Doppler-free I 2 calibration Ti:Sa MCP Beat-note measurement Nd:YAG 532 nm 899 Ti:Sa-cwring laser nm Nd:YVO 4 ; cw-pumplaser 532 nm R. Seiler, Th. Paul, M. Andrist and F. Merkt, Rev. Sci. Instr. 76, 1313 (25). Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

5 Results Observed Spectra: GK (v = 1, N = 1) 56p1 1 (S=, v + = ) 6 FWHM=8MHz signal intensity (arb. units) FSR= MHz FWHM = 19 MHz iodine etalon H 2 + exp H 2 + fit beam1 beam2 Quantification of Systematic Errors ac Stark shift (Ti:Sa laser) dc Stark shift (stray fields) frequency relative to iodine reference (MHz) Frequency shift (Ti:Sa laser) Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

6 Results Quantification of Systematic Errors: ac and dc Stark Shifts ac Stark Shift Using 4 µj.4(6) MHz dc Stark Shift Compensate electric stray fields to less than.6 mv/cm.(1) MHz ac Stark shift (MHz) H 2 + ion signal (arb. units) M N = M N = ± pulse energy (mj) applied electric field (mv cm -1 ) Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

7 Results Quantification of Systematic Errors: Frequency Shift and Chirp Resulting From the Pulsed Amplification in Ti:Sa Frequency shift and chirp 4 beat-note signal (arb. units) time relative to VUV and VIS laser (ns) Beyer, Sprecher, Merkt (ETH Zurich) 25 freq. shift (MHz) int. (arb. units) Caused by time-dependent changes of the refractive index of the Ti:Sa crystals during amplification.(5) MHz lifetime of the GK state time relative to VUV and VIS laser (ns) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

8 Results Quantification of Systematic Errors: Ion Induced Frequency Shift Statistics Stark shift caused by ions in the excitation volume Ions produced by photoionization of the GK state. Using 8 µj.(5) MHz H 2 + ion signal (arb. units) Statistics frequency relative to iodine reference (MHz) measurement.5.1 VIS pulse energy (mj).15 Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

9 Results Transition Frequency: GK (v = 1, N = 1) 56p1 1 (S=, v + = ) Shift Uncertainty (MHz) (MHz) Transition frequency relative to the I 2 reference line Position of the I 2 reference line [1] <.3 Shift by systematic errors.4.9 Shift by AOM s -96 <.1 Total [1] H. Knöckel, B. Bodermann and E. Tiemann, Software IodineSpec 5 (28). Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

10 Results Term Value and Ionization Energy of the GK (v = 1, N = 1) State Label Energy interval Frequency / MHz Wave number / cm 1 Reference (1) GK (v = 1, N = 1) 56p1 1 (v + =, S = ) (12) (4) This work (2) 56p1 1 (v + =, S = ) X + (v + =, N + = 1) (1) (3) [1] (3) GK (v = 1, N = 1) X + (v + =, N + = 1) (12) (4) This work (4) X (v =, N = ) X (v =, N = 1) (3) (1) [2] (5) X (v =, N = 1) X + (v + =, N + = 1) (11) (36) [3] (6) X (v =, N = ) GK (v = 1, N = 1) (12) (4) This work (1) [4] (17) [5] Ionization energy of the GK (v = 1, N = 1) state, determined as (1) + (2). Term value of the GK (v = 1, N = 1) state, determined as (4) + (5) (3). [1] D. Sprecher, Ch. Jungen, W. Ubachs and F. Merkt, Faraday Discuss. 15, 51 (211). [2] D.E. Jennings, A. Weber and J.W. Brault, J. Mol. Spectrosc. 126, 19 (1987). [3] J. Liu, E.J. Salumbides, U. Hollenstein, J.C.J. Koelemeij, K.S.E. Eikema, W. Ubachs and F. Merkt, J. Chem. Phys. 13, (29). [4] D. Bailly, E.J. Salumbides, M. Vervloet and W. Ubachs, Mol. Phys. 18, 827 (21). [5] Ch. Jungen, I. Dabrowski, G. Herzberg and M. Vervloet, J. Chem. Phys. 93, 2289 (199). Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

11 Conclusions and Outlook Conclusions and Outlook Measure GK term value New measurement: EF high-n interval by stimulated emission Acknowledgements X + high-n GK Ionization continuum 792 nm σ = 1.2 MHz 396 nm σ = 8.7 MHz HH _ Hansjürg Schmutz Joseph Agner EF Collaborators Wim Ubachs 179 nm σ = 12 MHz 22 nm σ = 5.4 MHz B Christian Jungen Financial Support European Research Council Swiss National Science Foundation X (a) (b) (c) Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11

12 Conclusions and Outlook Conclusions and Outlook Measure GK term value New measurement: EF high-n interval by stimulated emission Acknowledgements Hansjürg Schmutz Joseph Agner Collaborators Wim Ubachs Christian Jungen Financial Support European Research Council Swiss National Science Foundation H 2 + ion depletion signal (arb. units) relative frequency (MHz) Beyer, Sprecher, Merkt (ETH Zurich) 68th Int. Symposium on Molecular Spectroscopy June 17, / 11