Note on the Determination of Molecular Structure from Spectroscopic Data

Abstract

The problem of the change upon isotopic substitution of ``effective'' bond lengths and angles involving hydrogen is considered. Evidence is presented that in certain cases such variation is largely due to vibration of the heavy atoms rather than of the hydrogens. A method of calculating this effect is presented which utilizes a parameter similar to the ``quantum defect'' Δv=Ic—Ia—Ib observed in planar molecules. Estimates are given of the changes to be expected in effective hydrogen parameters upon isotopic substitution. Bond angles are found to slightly increase and bond lengths are found to decrease.