1. SOLVATION OF HCl, AGGREGATION OF H 2 O, HCl AND THEIR DEUTERATED ISOTOPES IN SUPERFLUID He DROPLETS GERHARD W. SCHWAAB, ÖZGÜR BIRER, ANNA GUTBERLET, MARKUS ORTLIEB, MARTINA HAVENITH Ruhr Universität Bochum 6/19/2008

2. Acids dissociate in aqueous solutions forming hydrogen (H + ) or oxonium/hydronium (H 3 O + ) ions. HA + H 2 O  H 3 O + (aq) + A - (aq) Definition of Acids (Arrhenius, 1884) n ?

3. IR Spectroscopy of Protonated Water Clusters H.A. Schwarz - J.Chem. Phys. 67 5525 (1977) Y.T. Lee - J. Phys. Chem. 94 3416 (1990) A.J. Stone - J.Chem. Phys. 110 6766 (1999) J.L. Kuo - Int. Rev. Phys. Chem. 24 553 (2005) M.A. Duncan, M.A. Johnson, K.D. Jordan - Science 308 1765 (2005), 304 1137 (2004) H 3 O + asym. str. 2665 cm -1

4. Microsolvation of HCl Farnik et al. - J. Chem. Phys. 118 10120 (2003) assignment difficult HCl / H 2 O HCl H2OH2O [cm -1 ] ln (I 0 / I)/10 -3 3200200028002400 0 0,5 1,0 1,5 2,0 2,5 (HCl) n≥1 (HCl) x (H 2 O) y (H 3 O) + (H 2 O) 3 Cl - HCl(H 2 O) 4

5. Microsolvation of HCl Masia et al. - J. Phys. Chem. A 111 12181 (2007) Odde et al. - J. Chem. Phys. 120 9524 (2004)

6. Microsolvation of HCl

7. Experimental Set Up-IR Spectroscopy d=5 um T N = 16 K P N = 50 bar HClH2OH2O Pick up QMS m/z ≥ 8 amu CW-OPO 2500-3400 cm -1 Nd:YAG MgO:LiNbO 3 0.38 K

8. Optically Selected Mass Spectroscopy QMS Scanning mass channels Fixed Frequency Nd:YAG MgO:LiNbO 3 m/z

9. HCl - nH 2 O moderate HCl pressure Different species?

10. HCl - nH 2 O Different species?

11. Optically Selective Mass Spectrum

13. DCl - nH 2 O 3 peaks 3 different species? Same spectral window

14. Formation of H 3 O + (H 2 O) 3 Cl - Masia, Forbert, Marx submitted

15. Conclusions Dissociation of HCl required 4 water molecules in helium environment. 2 spectral signatures of solvated hydronium are detected at 2670 cm -1. Strong evidence that the extra proton on hydronium does not originate from the acid.

16. Acknowledgements Forschergruppe: DPG-FOR 618 (Ha2394/13-1) Dominik Marx Group Ruhr University Bochum