Electrostatic deflection of the water molecule, a fundamental asymmetric rotor

An inhomogeneous electric field is used to study the deflection of a supersonic beam of water molecules. The deflection profiles show strong broadening accompanied by a small net displacement towards higher electric fields. The profiles are in excellent agreement with a calculation of rotational Stark shifts. The molecular rotational temperature being the only adjustable parameter, beam deflection is found to offer an accurate and practical means of determining this quantity. A pair of especially strongly responding rotational sublevels, adding up to \approx 25% of the total beam intensity, are readily separated by deflection, making them potentially useful for further electrostatic manipulation.