1. Infrared--Microwave Double Resonance Spectroscopy of Ar-DF (v = 0,1,2) Justin L. Neill, Gordon G. Brown, and Brooks H. Pate University of Virginia Department of Chemistry

2. Summary of Previous Work -Ground state Ar-DF rotational and hyperfine constants: -Keenan, Buxton, Campbell, Legon, and Flygare: JCP 74, 2133 (1981). -Dixon, Joyner, Balocchi, and Klemperer: JCP 74, 6539 (1981). -Infrared (v = 1), also Ar-HF v = 1 and v = 2 -Intermolecular potential of Ar-HF and Ar-DF by Hutson, JCP 96, 6752 (1992), reproducing all spectroscopic data available (mostly from the Nesbitt group). -Vibrational predissociation dynamics: -Ar-DF: -Oudejans, Nauta, and Miller: JCP 105, 10410 (1996) in v = 1 found a lifetime of at least 0.4 ms (by time of flight) -Ar-HF: -v = 1 observed to be metastable (lifetime > 0.4 ms) (Huang, Jucks, and Miller, JCP 85, 6905 (1986)) -v = 2 dissociation was faster than 0.3 ms (though not when observed in combination bands with the bending mode) (Block and Miller, CPL 226, 317 (1994)). -Higher overtone work by Klemperer

3. Instrumental Overview I) Balle-Flygare Fourier transform microwave spectrometer (based on NIST design) · Q factor ~ 10 3 -10 4 (theoretical S:N gain of ) · Low input power (~  W) required for optimal polarization · Can only see a very small part of the spectrum (~1 MHz) at one time · Relative intensities between lines unreliable (due to variable mode quality) T.J. Balle and W.H. Flygare, Rev. Sci. Instrum., 52, 33 (1981); R.Suenram, J.U. Grabow, A.Zuban, and I. Leonov, Rev. Sci. Instrum., 70, 2127 (1999).

4. Instrumental Overview II) 11 GHz chirped pulse Fourier transform microwave spectrometer · Collection of the 7.5-18.5 GHz rotational spectrum in a single data collection event · Phase stability allows for signal averaging in the time domain to match sensitivity of Balle-Flygare spectrometer in 10,000 averages · Relative intensities align well with predictions · Detecting weak IR absorptions is difficult (due to loss of sensitivity and shot-to-shot intensity fluctuations) G.G.Brown, B.C.Dian, K.O.Douglass, S.M.Geyer, and B.H. Pate. Rev. Sci. Instrum. (in preparation)

5. Experimental Procedure 3)Get high-resolution microwave spectra of rotational transitions in vibrationally excited states using Balle- Flygare cavity To observe deuterium quadrupole coupling 1)Find infrared absorption using the Balle-Flygare cavity Using double pulse ground state depletion technique 2) Find rotational transitions of vibrationally excited states using CP-FTMW spectrometer

6. 0.02 cm -1

7. Double Pulse Ground State Depletion MW pulse sequenceFID signalFourier transform

8. Vibrational Modes of Ar-DF v bk n D-F stretch bend van der Waals stretch

9. Ground State Depletion Scans · Monitor J = 2  1 in ground state (12157.56 MHz) · 20 time averages at each point, laser scan rate 0.003 cm -1 per second (2000)  (0000) (2110)  (0000) (  bend) band origin = 5703.52 cm -1 band origin = 5768.83 cm -1

10. Parity Selection Rules (2000) (0000)   J = 1 J = 0 J = 2 J = 3 e + e - e + e - J = 1 J = 0 J = 2 J = 3 e + e - e + e - PR (0000)J = 1 J = 0 J = 2 J = 3 e + e - e + e - (2110) J = 1 J = 2 J = 3 e - e + e - f + f - f + P QR · Only  transitions can have a Q branch because of the +  - parity selection rule. · For  transitions, the e parity upper state can only be accessed through the P or R branches,while the f parity state must be accessed through the Q branch. P.F. Bernath. Spectra of Atoms and Molecules. 2nd ed. Oxford University Press: Oxford, 2005.

11. Band Origins (vbkn)  (0000) Band origin (cm -1 ) (this work) Band origin (cm -1 ) (Hutson potential) (1000)2897.972897.98 (1001)2941.932941.90 (1110)2958.81 (1100)2958.98 (1111)2990.192990.23 (1101)2989.142989.11 (1200)2994.282994.26 (1003)2998.452998.43 (2000)5703.525703.61 (2110)5768.815768.99 J.M. Hutson, J. Chem. Phys., 96, 6752 (1992).

12. Band Origins (vbkn)  (0000) Band origin (cm -1 ) (this work) Band origin (cm -1 ) (Hutson potential) (1000)2897.972897.98 (1001)2941.932941.90 (1110)2958.81 (1100)2958.98 (1111)2990.192990.23 (1101)2989.142989.11 (1200)2994.282994.26 (1003)2998.452998.43 (2000)5703.525703.61 (2110)5768.815768.99 J.M. Hutson, J. Chem. Phys., 96, 6752 (1992).

13. Experimental Procedure 3) Get high-resolution microwave spectra of rotational transitions in vibrationally excited states using Balle- Flygare cavity 1)Find infrared absorption using the Balle-Flygare cavity Using double pulse ground state depletion technique 2) Find rotational transitions of vibrationally excited states using CP-FTMW spectrometer

14. Chirped Pulse--Fourier Transform Microwave Spectrometer Recently upgraded to 20 GS/s AWG (x8 circuit removed)

15. CP-FTMW Ground State Spectrum

16. IR-CP-FTMW Double Resonance Spectra

17. (e parity) pertubed by 2100 (f parity) unperturbed J = 3  2 GS J = 2  1

18. Rotational Constant Comparison (vbkn)B (this work)B (Hutson potential) (0000)3039.8533034.5 (1000)3048.7943042.9 (1001)3058.0093051.9 (1110) f2803.3142795.0 (2000)2967.8522971.8 (2110) f2982.1282980.6

19. Experimental Procedure 3) Get high-resolution microwave spectra of rotational transitions in vibrationally excited states using Balle- Flygare cavity 1)Find infrared absorption using the Balle-Flygare cavity Using double pulse ground state depletion technique 2) Find rotational transitions of vibrationally excited states using CP-FTMW spectrometer

20. Ar-DF Ground State 1000 time averages; 90  s gate on B-F cavity M.R. Keenan, L.W. Buxton, E.J. Campbell, A.C. Legon, and W.H. Flygare. J. Chem. Phys. 74, 2133 (1981). J = 2  1

21. Ar-DF Ground State 1000 time averages; 90  s gate on B-F cavity M.R. Keenan, L.W. Buxton, E.J. Campbell, A.C. Legon, and W.H. Flygare. J. Chem. Phys. 74, 2133 (1981). J = 3  2

22. Upper State Quadrupole Hyperfine (  states) The quadrupole coupling constant: · increases when energy is put into the D-F stretch · decreases when energy is put into the van der Waals stretch · The rotational constant follows the same trend.

23. Interpretation · Assuming structural properties of DF are preserved upon complexation-- a J.S. Muenter and W.Klemperer, J. Chem. Phys., 52, 6033 (1970).  StateB (MHz)D (kHz)  (kHz) 1/2 Free DF (GS)354.2 a (0000)3039.85359.6190.0(28)0.536(8)33.8 o (1000)3048.79455.7197(4)0.556(11)33.0 o (2000)3058.00952.0205(4)0.579(11)32.0 o (1001)2803.31488.5170.4(26)0.481(7)36.0 o two-line, two-parameter fit *Hutson predicts D = 61.5 kHz for (0000) and 57.3 kHz for (1000)

24. Conclusions · A total of ten vibrational bands were observed using the narrow-band FTMW as a detector of laser absorption · The rotational frequencies (using the chirped-pulse Fourier transform broadband microwave spectrometer) and deuterium quadrupole hyperfine constants (using the narrowband FTMW spectrometer) were observed in a total of six vibrational levels · The quadrupole coupling constant and rotational constant were both observed to increase upon excitation into the D-F stretch, and observed to decrease upon excitation into the van der Waals stretch · The quadrupole coupling constant increased upon excitation into the bending mode, but the rotational constant decreased, which appear to be contradictory results · No dissociation was observed in v = 1 or v = 2 based on linewidths and lifetime of FID (100  s)

25. Acknowledgements Pate Lab Funding: -NSF Chemistry and MRI program -Jefferson Scholars Foundation

26. Double Pulse Ground State Depletion Bloch Vector Model Initial “  /2”“-  /2”

27. Bending Modes 1110(e)

28. Bending Mode Interpretation StateB (MHz)D (kHz)  (kHz) 1/2 Free DF (GS)354.2 a (0000)3039.85359.6190.0(28)0.536(8)33.8 o (1000)3048.79455.7197(4)0.556(11)33.0 o (2000)3058.00952.0205(4)0.579(11)32.0 o (1001)2803.31488.5170.4(26)0.481(7)36.0 o (1110) (f)2967.85287.52270.64129.3 o (2110) (f)2982.12883.92330.65828.5 o ·  increases upon excitation of the bending mode, corresponding to a tightening of the van der Waals bond · This is contrary to the trend in the rotational constant