Infrared measurements and calculations on H2O.HO.

We have measured the infrared spectrum of H2O.HO in argon matrices at 11.5 +/- 0.5 K. We have also calculated the vibrational frequencies and intensities of the H2O.HO complex. As a result of these measurements and calculations, we have assigned a previously unassigned absorption band at 3442.1 cm-1 to the OH stretch in the radical complexed to the water molecule. This absorption originates from a complex that is situated in a different site within the argon matrix to those absorptions already assigned to this vibration at 3452.2 and 3428.0 cm-1. We observe a decrease in intensity of the OH radical stretching vibration of the H2O.HO complex upon isotopic substitution of D for H that agrees well with our calculations.