**************** The 15th., Lab Seminar *****************

Date: Mon, October 31, 2005  PM 1:30-

Place: No.616 Seminar room
　　　　　　 Graduate School of Information Science

Speaker: Norio Takenaka

Title: A theoretical analysis of the sum frequency generation spectrum 
of the water surface

Akihiro Morita, James T. hynes, Chemical Physics 258 (2000) 371-390.

 The present paper provides a theoretical analysis of the sum frequency
generation (SFG) spectrum of the water surface in the OH stretch mode
frequency region based on ab initio molecular orbital theory and molecular
dynamics simulation. the enviromental effects on the normal modes of OH
stretching vibration, their frequency shifts and hyperpolarizability are
formulated and tested. The simulated SFG spectrum reproduces experimental
results quite well. The surface susceptibilites of the dangling bond and
hydrogen-bonded bands have opposite signs in their imaginary parts, which
indicates opposite OH directions at the surface associated with these bands.
The former band turns out to be sensitive only to the top monolayer, and 
the latter band to a few top mololayers. Further analysis reveals that 
those two bands arise from quite types of molecular orientations. The 
assignment of the SFG spectrum is also analyzed in terms of the 
symmetric/antisymmetric character of the OH stretching modes and the degree 
of mode delocalization.

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