Knowledge Bank

The infrared spectrum (frequencies and intensities) of $H2O$ (monomer) has been calculated by the CNDO/2 approximate quantum-mechanical procedure, and compared with a more exact ab initio quantum-mechanical calculation, as well as with experimental $results.1$ Having calibrated the CMNO/2 calculation in this way we have then used it to calculate the expected Infrared spectrum for the linear and cyclic ($H2O)2$ dimers. A comparison of these results with experimental spectra confirms the assignment of the spectrum of the linear dimer in the $N2$ $matrix.2$ The calculation provides useful information about the changes in force constants and polar tensors that may be expected for an OH bond as it changes from free diatomic Oh to $H2O$ to ($H2O$)$\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}$.