  The rotational spectrum of the formaldehyde isotopologue H$_2$C$^{17}$O was
investigated between 0.56 and 1.50 THz using a sample of natural isotopic
composition. In addition, transition frequencies were determined for
H$_2$C$^{18}$O and H$_2$C$^{16}$O between 1.37 and 1.50 THz. The data were
combined with critically evaluated literature data to derive improved sets of
spectroscopic parameters which include $^{17}$O or H nuclear hyperfine
structure parameters.
