Millimeter Range Spectrometer for Studying Molecules and Weakly Bound Complexes in Supersonic Gas Jet

A design is presented for a millimeter-wave spectrometer used to study the rotational spectra of molecules and weakly bound molecular complexes in a supersonic gas jet. The spectrometer uses a highly stable microwave synthesizer (1–22 GHz) as a radiation source in combination with active frequency multipliers and covers the range 50–170 GHz. The gas flows out of the nozzle along the direction of the propagation of the radiation, which makes two passes through the vacuum chamber. To do this, the pulsed nozzle is placed in the center of the corner reflector, which receives the radiation. Absorption in the jet is detected by detector diodes with a Schottky barrier. The proposed scheme of the coaxial propagation of radiation and molecular beam provides better sensitivity and higher spectral resolution than the commonly used perpendicular configuration. The instrumental resolution of the spectrometer is 30–40 kHz, and the error in measuring the frequency is estimated at 3–4 kHz. The recorded spectra of rare CO isotopologues and weakly bound Ne–CO complexes demonstrate the capabilities of the new spectrometer.