Femtosecond Study of the Deuteron-Transfer Dynamics of Naphtol Salts in Water

We study the rate and mechanism of deuteron transfer from the photoacids 1-naphto1-4-sulfonate (1-NPS) and 2-naphtol-3,7-disulphonate (2-NPS) to acetate base in aqueous (D2O) solution. The photoacids are activated by excitation with 100 Is laser pulses at 267 am. The electronic absorption and stimulated emission spectra of the photoacid and the conjugate photobase and the vibrational absorption spectra of the hydrated deuteron and the acetate base are probed with broad-band delayed 100 fs pulses at visible and mid-infrared wavelengths, respectively. A significant fraction of the deuteron transfer events are observed to occur on a timescale of <1 ps within hydrogen-bonded contact photoacid-acetate complexes. For 1-NPS, this fraction is much higher than for 2-NPS. At later delay times, the reaction is dominated by deuteron transfer through short-living water wires of different lengths that connect the photoacid and the acetate base.