Paul Raston, Donald Kelloway, and Wolfgang Jäger Department of Chemistry, University of Alberta, Canada the OSU symposium, 2012 Infrared spectroscopy of HOCl embedded in helium nanodroplets 1

diffusion pump 8000 L / s turbo pump 700 L / s turbo pump 700 L / s turbo pump 700 L / s turbo pump 340 L / s Cryostat, 28 K skimmer 500 μm doping cell quadrupole mass-spec nozzle 5 μm 2 Helium Nanodroplet Isolation (HENDI) spectrometer

diffusion pump 8000 L / s turbo pump 700 L / s turbo pump 700 L / s turbo pump 700 L / s turbo pump 340 L / s Cryostat, 28 K skimmer 500 μm doping cell quadrupole mass-spec nozzle 5 μm 3 Helium Nanodroplet Isolation (HENDI) spectrometer

HOCl effusive mass spectrum Preparation: Cl 2 + H 2 O + HgO → HOCl + HgCl 2 + Cl 2 O +… H2OH2O N2N2 O2O2 CO 2 Cl 2 O HOCl 4

HOCl depletion spectrum in helium droplets Peak at ~ cm -1 is CO 2 HOCl a-type lines around 3609 cm -1 ; b-type feature around 3629 cm -1 Inset shows optically selected mass spectra 5

HOCl depletion spectrum: a-type region Asymmetric lineshapes suggests dynamical coupling of non superfluid helium to rotor 6 M.N. van Staveren, V.A. Apkarian, J. Chem. Phys., 133, (2010)

HOCl depletion spectrum: a-type region Asymmetric lines fit to FT of the time correlation, skew-type function, c(t)=exp(2  iv’t)exp(-2  t), where v’(t)=v c +  [1-exp(-2  t)] 7 M.N. van Staveren, V.A. Apkarian, J. Chem. Phys., 133, (2010)

Asymmetric lineshape analysis of OCS in helium droplets 8 S. Grebenev et al., J. Chem. Phys. 112, 4485 (2000); M.N. van Staveren et al., J. Chem. Phys. 133, (2010) Asymmetric lineshapes for OCS suggests that there is a chirp up in rotational frequency for R branch transitions and chirp down for P branch, occurring on similar tine scale to an initial rotational period c(t)=exp(2  iv’t)exp(-2  t), where v’(t)=v c +  [1-exp(-2  t)] The parameter  represents the damping of the rotationally excited state (Lorentz half- width) The parameters v c, , and  relate to the frequency chirp and represent the initial frequency, the chirp amplitude, and the damping of the chirp

Previous asymmetric lineshape analyses in helium droplets 9 S. Grebenev et al., J. Chem. Phys. 112, 4485 (2000); M.N. van Staveren et al., J. Chem. Phys. 133, (2010); A. Ravi et al., Phys. Rev. A 84, (R) (2011); P. L. Raston et al., PCCP 13, (2011)

HOCl depletion spectrum: a-type region Fits to sum (to account for HO 35 Cl and HO 37 Cl) of skew type functions much better than fits to Lorentzians 10

HOCl: Lineshape analysis 11 Mean response time of liquid helium following rovibrational excitation (J=2-1, v=1-0) plotted against the moment of inertia of He that is coupled to the rotor J' Ka'Kc' -J" Ka"Kc" v c (cm -1 )  (MHz)  (MHz)  (MHz) (3)-281(47)160(98)189(5) (25) (1)392(9)140(14)269(5) A. Ravi et al., Phys. Rev. A 84, (R) (2011); P. L. Raston et al., PCCP 13, (2011); S. Grebenev et al., J. Chem. Phys. 112, 4485 (2000); M.N. van Staveren et al., J. Chem. Phys. 133, (2010).

Caveat: HCN lineshape 12 HCN R(0)  Quantization axis Orientational Anisotropy

HOCl depletion spectrum: b-type region 13 Fit of , , , , , , and lines allows for determination of A constant = cm -1 It is reduced by only 1% relative to gas phase due to rotational dispersion

HOCl depletion spectrum: b-type region 14 b-type lines are much broader than a-type lines due to the greater density of droplet states available for relaxation of the excited rotational states. M. Hartmann, F. Mielke, J. P. Toennies, A. F. Vilesov, G. Benedek, Phys. Rev. Lett., 76, 4560 (1996)

HOCl (A) HOCl (B) HOCl: Rovibrational analysis 15 constantgas phase a He droplet v1v B" B'-B" A' b J' Ka'Kc' -J" Ka"Kc" Gas phase (cm -1 ) a He droplet (cm -1 ) b (1) (3) (2) (3) (1) b-type c (1) M.Y. Choi, G.E. Douberly, T.M. Falconer, W.K. Lewis, C.M. Lindsay, J.M. Merritt, P.L. Stiles, R.E. Miller, Int. Rev. Phys. Chem., 25, 15 (2006)

Summary and outlook Single HOCl molecules have been picked-up by superfluid helium nanodroplets with an efficiency of ~1% Rovibrational spectrum exhibits sharp, asymmetric peaks, which are accurately reproduced from fits to a chirped-damped oscillator function. From the fits, we have determined that the mean response time of liquid helium upon excitation of the R(1) transition for HOCl is 1 ns, which is 3- 4x faster than for the analogous transitions of OCS and CH 4 Rotational dispersion results in a relatively small renormalization of the A rotational constant, whereas this effect is not evident for rotations about the b- or c-axes (B constant is renormalized to 43% of its gas phase value). HOBr? 16

Acknowledgements Jäger group (UA) Xu group (UA) Marie van Staveren and Prof. V.A. Apkarian (UCI) Funding: Natural Science and Engineering Research Council of Canada Canada Foundation for Innovation Alberta Science and Research Investments Program 17