Martin Hepp

Phase locked backward wave oscillator pulsed beam spectrometer in the submillimeter wave range

We have developed a new submillimeter wave pulsed molecular beam spectrometer with phase stabilized backward wave oscillators (BWOs). In the frequency ranges of 260–380 and 440–630 GHz, the BWOs output power varies between 3 and 60 mW. Part of the radiation was coupled to a novel designed harmonic mixer for submillimeter wavelength operation, which consists of an advanced whiskerless Schottky diode driven by a harmonic of the reference synthesizer and the BWO radiation. The resulting intermediate frequency of 350 MHz passed a low noise high electron mobility transistor amplifier, feeding the phase lock loop (PLL) circuit. The loop parameters of the PLL have been carefully adjusted for low phase noise. The half power bandwidth of the BWO radiation at 330 GHz was determined to be as small as 80 MHz, impressively demonstrating the low phase noise operation of a phase locked BWO. A double modulation technique was employed by combining an 80 Hz pulsed jet modulation and a 10–20 kHz source modulation of the BWO...

High resolution Fourier transform spectroscopy of jet-cooled molecules

The spectroscopic literature reporting on the coupling between Fourier transform spectrometers and supersonic jet expansions is reviewed. Particular attention is devoted to high resolution infrared absorption experiments. Short and much longer introductions are provided on Fourier transform spectrometers and jets, respectively, with emphasis on the problems raised by coupling the two techniques. Details of the optical designs reported in the literature are considered. The literature on all the molecules studied is tabulated. Some of the spectroscopic results are highlighted, in particular those obtained at Universite Libre de Bruxelles.

SLIT-JET FOURIER TRANSFORM INFRARED SPECTROSCOPY IN 12C2H4 : COLD AND HOT BANDS NEAR 3000 CM-1

Abstract A Fourier transform interferometer was used to record the slit-jet absorption spectrum of 12 C 2 H 4 between 2500 and 3500 cm−1 at a spectral resolution of 0.02 cm−1. The rotational analysis of the ν9 and ν11 fundamental and ν2+ν12 combination bands is performed, effective rotational parameters are presented, and relative absorption intensities are measured. In addition, a few lines of the 2ν10+ν12 band are assigned. The selective sampling of vibrational hot bands in the jet is demonstrated using another experimental apparatus, with a heated slit.

A combined absorption–wavelength modulation technique for diode laser spectroscopy of van der Waals complexes in a pulsed planar jet

A tunable diode laser spectrometer modified for the investigation of molecular gases and van der Waals complexes in a supersonic jet is described. Simply constructed, reliable pulsed sources with 15 μm×(7–40 mm) slits were used at a repetition rate of the order of 100 Hz for the cooling of gases and for the formation of complexes. A double modulation technique based on a simultaneous modulation of the jet and a 10 kHz wavelength modulation of the diode laser enabled measurements of absorbances 1.3×10−5 (3×10−5 in relative absorption) at operating conditions corresponding to 1 s output time constant of the registration system. White type multireflection optics enlarged the absorption path of the laser radiation through the jet by 16 times. New spectra of the van der Waals complexes Ar–CH4 and Kr–CH4 in the 7 μm region are presented in order to show the characteristics of the spectrometer. The final resolution in the recorded spectra was better than 40 MHz. The rotational temperature of the complexes produc...

The Jet-Cooled Spectrum of Ethane Between 4000 and 4500 cm-1

The jet cooled infrared absorption spectrum of ethane was recorded from 4000 to 4500cm-1 using a high resolution Fourier transform interferometer (Bruker IFS120HR). The instrument resolution was 0.01cm-1, the rotational temperature obtained was around 40K. Ten combination bands were identified. Rovibrational assignments were performed, for the first time, concerning over 770 rovibrational lines. Band origins were obtained. Numerous perturbations are reported.

FOURIER TRANSFORM INFRARED JET SPECTROSCOPY USING A HEATED SLIT SOURCE

Abstract A supersonic slit-jet apparatus with a large heated slit nozzle apparatus used in combination with a high-resolution Fourier transform infrared spectrometer is described. The production of stable and reproducible expansions of samples, liquid under STP conditions, is demonstrated. The selective observation of vibrational hot bands is also achieved, with gas-phase species. The optimal available spectral resolution of the apparatus is illustrated.

The v6+v10 Band of Ethane

Abstract A Fourier transform interferometer was used to record the slit-jet cooled overtone absorption spectrum of ethane around 2.3 μm, at a spectral resolution of 0.01 cm −1 . The rotational temperature was determined to be 35 K. A band observed around 4343 cm −1 , of perpendicular type, was analysed. 139 lines were assigned to 7 different subbands. One of these subbands, K ′ ΔK = −2, shows torsional splittings. Effective rotational parameters were obtained for each subband. A strong perturbation obscures the K ′ ΔK = +1 subband, which thus could not be assigned. The vibrational band was assigned to the v 6 + v 10 combination band on the basis of the Coriolis ζ constant, which was found to be ζ 6+10 = 0.26(3). The band origin was determined to be v 6+10 0 = 4342.56(25) cm −1 .

Vibration-Rotation Bands in Ethane

The absorption spectrum of ethane was recorded at 0.014 cm−1 resolution in the range 4500–6500 cm−1 using a Fourier transform spectrometer and at room temperature. Eighteen bands could be identified and their type assigned. Upper state rotational constants are provided for the band at 5948.338 cm−1 and Coriolis constants are obtained for most perpendicular bands. Vibrational assignments are suggested for the bands at 5948 cm−1 (v7 + v10), 5914 cm−1(v8 + v 10+ v 11), and 5852cm−1 (v 5+v 10). All vibrational bands reported in the literature are gathered.