Knowledge Bank

Ab initio MO calcutations of infrared intensities of $H2O$ predict infrared intensities for the fundmental modes that differ considerably from the reported experimental values. Even when these calculations are made at the highest level of theory (the dipole derivatives were calculated with a very large basis set, using fourth order MBPT and CCSD + T(CCSD)) the predictions for the intensity of $\nu 1$ and for $\nu 2$ are too high, compared with experimental values. This discrepancy has inspired us to measure relative intensities of these fundamental modes for samples of $H2O$ isolated in Ar, $N2$ and CO matrices. The results will be discussed critically in an attempt to resolve the discrepancy between theory and experiment for this important test $molecule.