Laser-initiated Shuttling of a Water Molecule Between H-bonding Sites

The two-step laser excitation scheme of stimulated emission pumping (SEP) induces shifts of a single water molecule between two remote hydrogen bonding sites on trans-formanilide. This reaction can be initiated by selective excitation of either isomer (CO-bound or NH-bound) with different SEP excitation wavelengths. Energy (E) thresholds for isomerization in both directions have been measured [796 wave numbers </= E(CO-->NH) </= 988 wave numbers and 750 wave numbers </= E(NH-->CO) </= 988 wave numbers], and the energy difference DE between the CO-bound and NH-bound isomers was extracted (-238 wave numbers </= DE </= +192 wave numbers).