High Resolution Molecular Spectroscopy Group: Spectrometers

Millimeter-Wave Spectrometer (50 - 650 GHz)

The radiation sources are Gunn oscillators which operate between 50 and 115 GHz. Higher frequencies are produced by means of multipliers. The oscillators are frequency modulated and phase-locked to the reference signal delivered by a synthesized generator. A Schottky-barrier diode and a liquid-Helium-cooled InSb bolometer are used as detectors. The absorption cell is a 4 m long, 5 cm i.d. glass cell equipped with cilindrical electrodes which allow for the production of unstable species by means of a negative glow discharge. The cell can be cooled down to 77 K, and a longitudinal magnetic field can be applied.

Recording of the J = 1 - 0, K = 0 rotational transition of the ³⁴SD₃⁺ molecular ion, which was produced in a glow discharge using a gaseous mixture of D₂S, D₂ and Ar, at 110 K. The transition is clearly visible (upper trace) when a longitudinal magnetic field of ca. 100 G is applied. The rotational line disappears (lower trace) when the magnetic field is off.
[L.Dore et al., Chem. Phys. Lett. 300, 489 (1999)]

Sideband FIR Spectrometer

It is based on a passive FIR laser optically pumped by a CO₂ laser. The FIR emission is mixed with the radiation produced by a tunable microwave source, and the resulting sidebands are used to record the spectra in the FIR region. The weak sidebands are separated from the strong FIR emission through a Michelson interferometer.

Sub-Doppler recording of the J = 58 - 57 rotational transition of OCS, obtained using the Lamb-dip technique and a Fabry-Perot cavity as absorption cell. The FIR carrier was given by a formic acid emission line. The first derivative of the actual absorption profile is displayed.
[G.Cazzoli et al., J. Molec. Spectrosc. 151, 378 (1992)]

Diode-Laser Infrared Spectrometer

The sources are lead-salt diodes, operating at a temperature of few tens of Kelvin degrees. The spectrometer is in its triple beam configuration, so that sample spectrum, reference spectrum, and etalon fringes can be simultaneously recorded.

	The reference gas spectrum (N₂O).
	Etalon fringes. The separation is ca. 0.0097 cm^-1.
	Spectrum of BrC¹⁵N in the region of the v₃ band. The isotopic splittings between the ⁷⁹Br and ⁸¹Br lines are clearly resolved. [C.Degli Esposti et al., J. Molec. Spectrosc. 174, 59 (1995)]