Experimental measurement of the induced dipole moment of an isolated molecule in its ground and electronically excited states: Indole and indole- H2 O

Reported here are measurements of the magnitude and orientation of the induced dipole moment that is produced when an indole molecule in its ground S0 and electronically excited S1 states is polarized by the attachment of a hydrogen bonded water molecule in the gas phase complex indole- H2 O. For the complex, we find the permanent dipole moment values μIW (S0) =4.4 D and μIW (S1) =4.0 D, values that are substantially different from calculated values based on vector sums of the dipole moments of the component parts. From this result, we derive the induced dipole moment values μI* (S0) =0.7 D and μI* (S1) =0.5 D. The orientation of the induced moment also is significantly different in the two electronic states. These results are quantitatively reproduced by a purely electrostatic calculation based on ab initio values of multipole moments.