A new Stark-modulated submillimeter-wave spectrometer is described. This spectrometer has been used to analyze the microwave spectrum of three isotopomers (heavy atoms) of ketene. The rotational constants determined have been used to calculate the structure of ketene using a variety of methods. The question of planarity of ketene is also addressed. High-resolution microwave measurements have been used to determine the spin-rotation interaction in CH2 13CO.