Knowledge Bank

Rotational spectra of $H2CO-H35CI,H2CO-H37CI,D2CO-H35CI$, and $D2CO-H37CI$ have been observed using a pulsed nozzle Fourier transform microwave spectrometer. For $H2CO-H35CI$ the following spectroscopic constants have been determined (in MHz): $B=2687.856(23),C=2527.412(23),\Delta J=0.0105(12),\Delta JK=0.223(10),eQqaa=-41.424(14)$ and $eQqbb=14.106(19)$. The $HCl$ subunit is bonded to the oxygen of the $H2CO$ subunit through a non-linear hydrogen bond. For the $H2CO-H35C1$ complex, the distance between the centers of masses of the two units is 3.3487 A giving an O--Cl distance of 3.22 A. From the quadrupole coupling constant, $eQqaa$, an effective vibrationally averaged angle between the HC1 axis and the axis of the complex is determined to be $30.5\circ$. Centrifugal distortion analysis yields estimates of the weak bond stretching force constant and stretching frequency as 0.069(8) mdyn/A and $85(4)cm-1$ respectively. The structural results are compared with the predictions of Buckingham and $Fowler1$ from their electrostatic model.