Rydberg spectroscopy of Zeeman-decelerated beams of metastable Helium molecules

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1 Rydberg spectroscopy of Zeeman-decelerated beams of metastable Helium molecules Paul Jansen, Michael Motsch, Daniel Sprecher, Frédéric Merkt Laboratorium für Physikalische Chemie, ETH Zürich

2 Motivation 2-electron molecule 3-electron molecule E( ) =E (0) + 2 E (2) + 3 E (3) + 4 E (4) +...

3 Previous studies of He2 + He 2 + has no dipole moment or easily accessible electron states Very little experimental data available; - 9 rovibrational v = 0 1 transitions in 3 He 4 He + (uncer. 18 MHz) [1] - 7 rovibronic X A (v =22,23 0,1) transitions in 4 He 2 + (uncer MHz) [2] Alternative: Rydberg spectroscopy long lived (13s) [1] Yu and Wing, Phys. Rev. Lett. 59, 2055 (1987). [2] Carrington et al., J. Chem. Phys. 102, 5979 (1995).

4 Rydberg states of atoms and molecules = E+ i ( +,N + ) hc R M (n µ`) 2 Ionisationcontinuum n = + v =0 + N =0 + v =0 + N =1 + v =0 + N =2 Energy n=53 l=0-52 n=52 l=0-51 n=51 l=0-50 n=53 n=52 n=51 n=50 l=0-49 H-Atom l=0 l=1 l=2 l=3,...,n-1 Other Atoms n=50 Molecules

5 ZEKE spectroscopy of He2 * Accuracy of ~ 1 GHz PFI-ZEKE spectrum Energy Ionnization window Rydberg states Laser wavenumber Signal [1] Raunhardt et al., J. Chem. Phys. 128, (2008).

6 Extrapolating Rydberg series with MQDT ν = E+ (v +,N + ) hc R He 2 (n µ) 2 anck s constant, N c + =5 is the (6) speed of energy 0 N + =3 N (3) =1 Sprecher et al. [1] N =1 N =3 N =5 Fosca et al. [2] Accuracy ~ 100 MHz (Doppler limited) [1] Sprecher et al., J. Chem. Phys. 140, (2014). [2] Fosca et al., J. Mol. Spectrosc. 191, 209 (1998).

7 7 mm

8

9 ) Energy / hc (cm Magnetic field (T)

10 ) Energy / hc (cm Magnetic field (T) ~F Z = dw Z dr ~ ~

11 ) Energy / hc (cm Magnetic field (T) ~F Z = dw Z dr ~ B µ ~

12 Multistage Zeeman deceleration Vanhaecke et al., Phys. Rev. A 75, (R) (2007). Hogan et al., Phys. Chem. Chem. Phys. 13, (2011).

13 Multistage Zeeman deceleration Potential energy of a low-field seeker Vanhaecke et al., Phys. Rev. A 75, (R) (2007). Hogan et al., Phys. Chem. Chem. Phys. 13, (2011).

14 Multistage Zeeman deceleration Phase angle determines energy removed per stage Vanhaecke et al., Phys. Rev. A 75, (R) (2007). Hogan et al., Phys. Chem. Chem. Phys. 13, (2011).

15 Multistage Zeeman deceleration Vanhaecke et al., Phys. Rev. A 75, (R) (2007). Hogan et al., Phys. Chem. Chem. Phys. 13, (2011).

16 Multistage Zeeman deceleration Switching of magnetic field takes 8.5 μs [1]: Supersonic beam of pure He at 300 K too fast (1900 m/s) Seeding not possible due to Penning ionisation 2.5 Magnetic field (T) Rise and fall time 8.5 µs Time (µs) [1] Wiederkehr et al., J. Chem. Phys. 135, (2011).

17 Cryogenic source of He2 * beam

18 Cryogenic source of He2 * beam discharge electrode valve body (10K) thermal shield (77K) filament

19 Beam characterization

20 Beam characterization velocity distribution rotational temperature

21 Experimental setup cryogenic reservoir discharge electrodes valve skimmer mcp detector Zeeman decelerator ionization laser extraction electrodes

22 Deceleration results H e + 2 ion signal (arb. units ) m/s 150 m/s 135 m/s 120 m/s Motsch et al., Phys. Rev. A 89, (2014). Delay (ms)

23 Rydberg spectroscopy of decelerated He2 * 3.0 H e + 2 ion signal (arb. units ) m/s x3 500 m/s Wave number (cm -1 ) Motsch et al., Phys. Rev. A 89, (2014).

24 Rydberg spectroscopy of decelerated He2 * N + = H e + 2 ion signal (arb. units ) N + = N + = N + = N + = N + = m/s x3 500 m/s Wave number (cm -1 ) Motsch et al., Phys. Rev. A 89, (2014). notation: N 00! np N + = N 00 (N=N + )

25 State selectivity of deceleration! No rotational-state selectivity One spin-rotational component (J = N) rejected 250 N= ) -1 hc (cm J=0 J=2 Energy / N=3 N= Magnetic field (T) J= Magnetic field (T)

26 Conclusion & Outlook Efficient production of a beam of He2 * Zeeman deceleration to 100 m/s Many states decelerated simultaneously Phase-space density sufficiently high for spectroscopy

27 Acknowledgements mechanical support: Anton Josef Agner!!! electronic support: Hansjürg Schmutz