The rotational constant A0 and planarity of the hydrogen-bonded complex H2CO⋯HCl
Abstract
A fit of µa, R-branch transitions of the nearly prolate asymmetric rotor H2CO⋯HCl (κ≈–0.99) demonstrated that even a relatively large A0 rotational constant can be determined with useful accuracy from such a limited set of data, provided the frequencies are of sufficient accuracy. Thus the set of spectroscopic constants A0, B0, C0, ΔJ, ΔJK, δJ, χaa, (χbb–χcc), χab and ½{Mbb+Mcc} are reported for H2CO⋯H35Cl. The subsequent observation of two µb, R-branch transitions led to a much more accurate value of A0, but this did not lie outside the error of the preliminary value, confirming the usefulness of the initial approach. The inertial defect Δ0= 0.5724(1) u Å2 demonstrates that the nuclei in H2CO⋯H35Cl are copolanar. Fits of limited numbers of µa, R-branch transition frequencies for each of H2CO⋯H37Cl, D2CO⋯H35Cl and D2CO⋯H37Cl led to Δ0 values for the isotopomers identical within experimental error to that of H2CO⋯H35Cl.