Microwave Spectrum of Formaldehyde II. Molecular Structure in the Ground State

Abstract

Rotational constants for the isotopic formaldehyde molecules H₂CO, H₂C¹³O, H₂CO¹⁸, HDCO and D₂CO were determined from the parameters used in the analysis of K-type doubling spectra and the frequencies of 1₀₁←0₀₀ transitions. In the cases of isotopic species for which the R-branch transitions were not measured, the calculated inertia defect was used in the determination of the rotational constants.
From the rotational constants, the zero-point structure of formaldehyde molecule, r_z, was determined by a new method taking into account the zero-point vibration-rotation interaction and electronic interaction. The following zero-point molecular structure was obtained;
r_C–H=1.117₄±0.002 A
∠HCO=122°5’±20’
r_C=O=1.206_3±0.002Aplanar.
Alloftherotationalconstantscalculatedfromthesegeometricalparametersfittotheobservedvalueswithintheexperimentalerror.Incontrasttothepreviousresearches,∠HCOismuchlargerthan120°.Itwasalsoconfirmedthattheformaldehydemoleculeiscompletelyplanarinthegroundvibrationalstate.