1. The 65th International Symposium on Molecular Spectroscopy, June 21-25, 2010
Hydrated HCl Complexes, (HCl)m(H2O)n, in Helium Nanodroplets: OH Stretching Modes
( )m
( )n
Seung Jun Lee, Myong Yong Choi
Gyeongsang National University, Jinju, Korea
Dimitry Skvortsov and Andrey F. Vilesov
University of Southern California, Los Angeles, CA 90089, U.S.A.

2. Solvation of HCl by Water- +
completely ionized
more water added ?
How many water molecules are needed to dissociate HCl?
What are the structures of HCl-water clusters?
Role of hydrogen bonding?

3. Calculations of HCl-Water Clusters
Packer, Clary, J.P.C. 1995
Sobolewski, Domcke, PCCP 2005
Chaban, Gerber, Janda, JPCA 2001

4. Calculations of HCl-Water Clusters
(12.5)
Calculations of HCl-Water Clusters
(0.4)
(2.5)
(w/ ZPE in kJ/mol)
MP2/aug-cc-pVDZ
(0)
n = 1 2 3 4
(-3.2)

5. (HCl)m(H2O)n clusters in Ar matrix
b-OH
f-OH
Amirand, Maillard, J. Mol. Struct. 1988

6. FTIR spectra (HCl)m(H2O)n clusters in free jet
Devlin, Farnik, Suhm, Buch,
J. Phys. Chem. A, 2005
HCl
HCl
b-OH
f-OH
There is still lack of distinguishing the stretching of HCl between physisorbed and dissociated HCl molecules in previous studies. There are many exp. which was done on the surface of ice
Farnik, Wiemann, Suhm, JCP 2003
The clear assignment of the hydrated HCl with four water molecules is not still available through spectroscopy.

7. Laser Depletion Spectroscopy
Ultra Low Temp.
(0.37K for 4He)
HCl
Pick-up
Chamber
Main chamber
Closed-cycle
refrigerator
Nozzle
LN2 trap
Power meter
Quadrupole
X-Y-Z
H2O pick-up cell
Nd:YAG
1064 nm, 750 mJ, 7 ns
OPO/OPA
cm-1
≈ 1 m
Wie koennen heir die Helium Tropfchen hielfen?
Wir bielden die Cluster in He Troepfhen in einem suksessiven Einfang der Molekuelen.
Es ist wichtig, dass den Einfang Quersnitt bleibt ungefaer konstant fuer die erste und die zweite Molekuel. Deshalb Kennen wir die relativen Besetzung von Monomeren und Clustern im Strahl.

8. IR Spectra of (HCl)m Clusters
Spectral assignment of (HCl)n clusters up to n = 6
Cyclic structures up to the hexamer
Frequency saturation for large clusters
Spectroscopists do it with frequency and intensity
Skvortsov, Choi, Vilesov, JPCA 2007

9. Pick up of molecules by He droplets
Abundance of Mn follows Poisson distribution:
z – average number of pickup collisions, linear with pickup pressure

10. Overview Spectra in He droplets
Neat
(HCl)m and (H2O)n
clusters
HCl
b-OH
f-OH
m = 4 2 3 1
n = 6 5 3+
Mixed
HCl and H2O
clusters
Skvortsov, Choi, Vilesov, unpublished 2007

11. Free OH-stretch bands in water and small HCl-H2O clusters
<0>
<3>
<2>
<2>
<1>
<3>
<1>
<2>
<1>
<2> *
<1>
<1>
<0.5>
<2>
<1>
<0.5>
(H2O)2
H2O
<0>
<0.5>
<0>
<2>

12. Free OH-stretch bands in water and small HCl-H2O clusters
Skvortsov, Choi, Vilesov, JPCA 2009

13. Free OH-stretch bands in water and larger HCl-H2O clusters
Free OH bands of larger (HCl)m(H2O)n clusters are not resolved
Skvortsov, Choi, Vilesov, JPCA 2009

14. Overview Spectra in He droplets
Neat
(HCl)m and (H2O)n
clusters
HCl
b-OH
f-OH
Mixed
HCl and H2O
clusters
Skvortsov, Choi, Vilesov, unpublished 2007

15. Bonded OH-stretch bands in water and (HCl)m(H2O)n clusters
: Assignment in Progress
2w: *
1h: *
3w: #
2h: #
<HCl>
<H2O>
<HCl>
<H2O> # # #
<3>
<2> #
<2>
<1> * *
<1> * *
<2> * * *
<1>
<2>
<0.7>
<2>
<0.35>
<2> 1w
<1> 5 4 3 2
<2>
<1> 1w
<0> 6 6
(H2O)n

16. Conclusions
(HCl)1(H2O)1-3 and (HCl)2(H2O)1 clusters were identified by IR depletion spectroscopy using helium droplet matrix: Free OH stretching region
The congestion of the larger cluster bands makes the assignments of the clusters having more than 4 water molecules difficult

17. Andrey F. Vilesov Group at USC GNU Laser Spectroscopy Lab.
Acknowledgements
Andrey F. Vilesov Group at USC
GNU Laser Spectroscopy Lab.