The vibrational Stokes shift of water (HOD in D2O) |
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Authors: | Wang Zhaohui Pang Yoonsoo Dlott Dana D |
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Institution: | School of Chemical Sciences, University of Illinois at Urbana Champaign, Urbana, Illinois 61801, USA. |
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Abstract: | The vibrational Stokes shift of the OH stretching transition nu(OH) of water is the shift between the ground-state absorption and the excited-state (v=1) emission. A recent measurement on HOD in D(2)O solvent S. Woutersen and H. J. Bakker, Phys. Rev. Lett. 83, 2077 (1999)] of a 70 cm(-1) redshift, and a subsequent calculation of a 57 cm(-1) redshift using equilibrium molecular dynamics simulations C. P. Lawrence and J. L. Skinner, J. Chem. Phys. 117, 8847 (2002)] were in good agreement. We now report extensive measurements of the vibrational Stokes shift in HOD/D(2)O using an ultrafast IR pump, Raman probe method. The vibrational Stokes shift is seen to depend on the pump pulse frequency and on time delay; by varying these parameters it can be made to range from 112 to -32 cm(-1) (negative values indicate a blueshift in the excited state). The equilibrium vibrational Stokes shift is actually a negative rather than a positive quantity. Possible reasons for the disagreement between experiment and theory are briefly discussed. |
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