Analysis of time-resolved anisotropy of transient absorption enabled determination of room temperature ground and excited state rate constants for intramolecular double hydrogen transfer in two similar porphycenes, one of them with symmetric and the other, with asymmetric character of a double minimum potential for hydrogen motion. The perturbation preserves a quasi-symmetric minimum in S(0), but the rate decreases approximately two times. In S(1), the perturbed potential becomes strongly asymmetric, and the downhill hydrogen transfer occurs with a rate higher than that observed for a symmetrical compound.
We
have observed for the first time the surface-enhanced (SE) signal
of water in an aqueous dispersion of silver nanoparticles in spontaneous
(SERS) and femtosecond stimulated Raman (SE-FSRS) processes with different
wavelengths of the Raman pump (515, 715, and 755 nm). By estimating
the fraction of water molecules that interact with the metal surface,
we have calculated enhancement factors (EF): 4.8 × 10
6
for SERS and (3.6–3.7) × 10
6
for SE-FSRS.
Furthermore, we have tested the role of simultaneous plasmon resonance
and Raman resonance conditions for the a
ν
1
+ bν
3
overtone mode of water (755 nm) in
SE-FSRS signal amplification. When the wavelength of the Raman pump
is within the plasmon resonance of the metal nanoparticles, the Raman
resonance has a negligible effect on the EF. However, the Raman resonance
with the a
ν
1
+ bν
3
mode strongly enhances the signal of the fundamental OH stretching
mode of water.
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