Depletion modulation of Ar–H2O in a supersonic planar plasma

A sensitive detection technique for tunable diode laser spectroscopy is presented that is suited to study rotationally resolved spectra of weakly bound complexes. The method uses a low energetic plasma source to achieve an efficient concentration modulation in a supersonic planar jet expansion. The method is demonstrated with rotationally resolved spectra of the Π(110)←Σ(101) and Π(212)←Σ(101) internal rotation/vibration bands of ortho Ar–H2O in the ν2 bend region of H2O. The latter transition has not been reported before and is recorded at 1658.0309(6) cm−1.