Structural Evolution & Solvation of OH radical in (H2O)n

+, n=5~8

En-Ping Lu, Piin-Ruey Pan, Ying-Cheng Li and Jer-Lai Kuo Institute of Atomic and Molecular Sciences,

Academia Sinica, Taipei, Taiwan

Ming-Kang Tsai

Dept of Chem., National Taiwan Normal University,

Taipei, Taiwan

69th OSU Int. Symp. on Mol. Spectroscopy,University of Illinois Urbana-Champaign, USA, June/19/2014

(H2O)2+: Proton Transferred (PT)

or Hemi-Bonded (HB)

Pan et al. PCCP, 14, 10705 (2012)

PT HBTS

DE (kcal/mol) PT TS HBBLYP 0.00 -7.27B3LYP 0.00 7.51 0.27BH&HLYP 0.00 16.41 10.86MP2 0.00 18.79 13.92CCSD(T) 0.00 15.14 8.80

(H2O)n+ vs. H+(H2O)n

Mizuse, Kuo, Fujii, Chem. Sci., 2, 868 (2011)

(H2O)n+, n=3~8 w/o Ar

Mizuse, Kuo, Fujii, Chem. Sci., 2, 868 (2011)Mizuse & Fujii, J. Phys. Chem. A., 117, 929 (2013)

Spectra w/o Ar differ for n=7 (temp?)Many isomers contribute to spectra

How to generate Structures (1)?

• Basin-Hopping MC algorithm + B3LYP/6-31+G*Do & Besley J. Phys. Chem. A., 117, 5385 (2013)

• Refined MP2/6-311++G**

How to generate Structures (2)?

H+(H2O)n (H2O)n

(H2O)n+

The similarity of H-Bond network Ionization process

e-

(H2O)n: Nguyen, Ong, Kuo, J. Chem. Theory Comp., 5, 2629 (2009).H+(H2O)n: Nguyen, Ong, Soh, Kuo, J. Phys. Chem. A, 112, 6257 (2008)

Re-optimized by BH&HLYP/aug-cc-pvDZ& B3LYP/6-31+G* (for comparison)

• Our 1st-Principle Search Method

Diff. Structures of (H2O)n+,

n=5~8

We found more stable isomers than Besely for n=7 & 8.

Energy of (H2O)n+, n=5~8

Many isomers with similar energy, proper sampling is needed.

Taking Statistical Averages

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Harmonic Superposition Approximation(HSA)

Contribution from ALL isomers can be computed by HSA.

For relevant temp. only a sub-set is needed.

Topology of (H2O)n+ at diff. Temp.

Structure/Topology of clusters are sensitive to temperature.

Coordination # of OH radical

Coord. # of OH radical is more than 1 for n=6, 7 & 8.

IR Spectra of (H2O)7+ w/o Ar

Two new vib. bands assigned + Temp-dep. features captured.

IR Spectra of (H2O)n+, n=5~8

• Vib. band ~ 3200 cm-1 is assigned to fully solvated OH.• Direct evidence of solvated OH radical for n ≥ 7.

• For n ≤ 5, OH prefer to stay at terminal site. Fully solvated OH appears at n ≥ 6, dominates for n ≥ 7.

• PT is Hm more stable (~ 10 kcal/mol). Be careful with the Exc used.

• Vib. band ~ 3200 cm-1 is assigned to fully solvated OH.

Conclusion

• Energy Landscape of (H2O)n+ is rough,

Proper sampling of structures is required/important.

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