(Color online) Schematics of the stretching modes and transitions relevant for pump-probe experiments. The notation stands for three quantum numbers associated with the symmetric stretch, bend, and asymmetric stretch of the H–O–H molecule, respectively. The bending mode has no relevance to the presented experiments. The energies of transitions and level assignments are the results of calculations.
(Color online) Absorption spectra of (blue) and HDO (orange) molecules dissolved in acetonitrile (green). In (b), the spectrum is corrected for the solvent contribution. The excitation pulse spectrum is shown by solid dots. The red dashed curve depicts the simulated absorption spectrum.
(Color online) (a) Isotropic transients at several representative frequencies and (b) transient spectra at delay. The inset in (a) shows transients for orthogonal pump and probe polarizations. The transients in (a) are obtained around the central frequencies of the symmetric (, green) and asymmetric (, blue) modes near the transition (, red) and at the maximum of the induced absorption (, black, the sign is reversed). Black vertical lines in (b) show positions and intensities of the transitions contributing to the pump-probe signal. In (b), the blue dots show the experimental, and the red solid curve the calculated isotropic pump-probe spectra at a delay.
(Color online) Experimental (blue dots) and simulated (red solid curve) transient anisotropy spectra at a delay. Note the decrease of anisotropy to 0–0.2 values within the first for most frequencies. The breaking point around is due to the zero amplitude of the isotropic transient spectrum at this frequency [Fig. 3(b)].
(Color online) Transient anisotropies at the same frequencies as in Fig. 3(a): experimental transients at (a) short and (b) long delays and (c) calculations. The orange triangles in (a) and (b) show the HDO in acetonitrile data measured at , i.e., near the absorption maximum; the rest of the transients are for in acetonitrile. The lines in (a) and (b) show a monoexponential fit to the experimental data at long delays with the time constant that reflects the true rotational anisotropy decay. This process is not included in simulations in (c).
The parameters used in modeling.
The calculated transition frequencies (in ) in the stretching mode region. The numbers in parentheses are the relative transition intensities and the transition dipole direction with the axis oriented along the axis and the axis out of the molecular plane. The numbers are given for the asymmetry parameter and scaling coefficient .
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