Knowledge Bank

A vibrational analysis has been carried out for HCOOH, DCOOH, HCOOD, DCOOD, and for $HCOOCH2$, $DCOOCH3$, $HCOOCD3$, $DCOOCD3$. The infrared spectra of $DCOOCD3$ were obtained and assigned. Calculations were performed with (I) a simplified valence-type force field, (II) a valence-type force field with CO stretching constants estimated from bond length data, and (III) a Urey-Bradley force field. The simplified valence force field (I) contained 30 parameters and after refinement reproduced 90 observed frequencies with an average error of $5.7cm-1$ or 0.6%; the obtained values for CO stretching force constants were in good agreement with estimations based on bond length data. If the latter constants were in good agreement with estimations based on bond length data. If the latter constants are not submitted to refinement (calculation II) it is possible to obtain numerical values for additional off-diagonal constants, while the computational uncertainty remains low. A Urey-Bradley force field (calculation III) produced an average frequency error of $8.1cm-1$ and slightly higher computational uncertainties. If transformed into valence coordinate space, the results of this calculation lead to CO stretching force constants which differ somewhat from calculations (I) and (II).