R. Gendriesch

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...

Interstellar Detection of CCC and High-Precision Laboratory Measurements near 2 THz

We describe more fully our original tentative interstellar detection of the triatomic pure carbon chain molecule, CCC, in absorption toward the Galactic center source Sgr B2. C3 was detected with the Kuiper Airborne Observatory (KAO) by observing the R(2) bending vibration-rotation transition (0, 1 1 ,0 0, 0 0 , 0) near 65.7 cm 1 during one ) R ( of the last flights of KAO. The R(2) absorption line detected toward Sgr B2 is centered at 63.7(5) km s 1 , with km s 1 and a peak absorption of 18(3)%. This original tentative interstellar detection of C 3 DV(FWHM)p 8.3(9) has recently been confirmed by J. Cernicharo et al. through observation of a total of nine absorption lines, including the same R(2) line with the Infrared Space Observatory . We also present highly precise new laboratory measurements of 10 rovibrational transition frequencies of the n2 bending mode of C3, which have been obtained with the Cologne Sideband Spectrometer for Terahertz Application. Subject headings: ISM: individual (Sagittarius B2) — ISM: molecules — line: identification — methods: laboratory — techniques: spectroscopic On-line material: color figure

Terahertz Spectroscopy of Linear Triatomic CCC: High Precision Laboratory Measurement and Analysis of the Ro-Vibrational Bending Transitions

We report concise measurements of the bending vibration transition (0,11,0) ← (0,00,0) near 63.416529(40) cm−1 of the carbon cluster CCC in the electronic ground state (X1Σ+g ). The ν2 vibration- rotation spectrum consists of P-, Q-, and R-branch transitions. A total of ten ro-vibrational transitions have been measured with the Cologne Sideband Spectrometer for Terahertz Applications, COSSTA. It is essentially a Backward Wave Oscillator (BWO) based, and frequency stabilized sideband spectrometer. The essential feature of COSSTA is the absolute frequency accuracy of the measurements. Absolute frequency calibration is better than 5 kHz at 2 THz, i. e. COSSTA reaches microwave accuracy. The band centre frequency was determined to be 1.901181506(162) THz: The derived molecular parameters are: (0,00,0) : B = 12908.242(142) MHz; D = 44.30(40) kHz; H = 4.068(184) Hz; (0,11,0) : B = 13262.946(109) MHz; D = 70.33(39) kHz; H = 7.71(38).

FREQUENCY LOCK OF AN OPTICALLY PUMPED FIR RING LASER AT 803 AND 1626 GHz

We report an automatic frequency control (AFC) for an optically pumped far infrared (FIR) ring laser applicable for high resolution THz sideband spectroscopy by mixing a fraction of the laser power and a harmonic of a phase-locked synthesizer on a planar Schottky diode. We achieve a relative frequency accuracy of about 0.5 kHz rms at 803 GHz (15NH3) and about 1 kHz rms at 1626.6 GHz (CH2F2) over hours of lock time. The absolute frequency accuracy is estimated to be about 5 kHz at 1626.6 GHz.

Sub-Doppler Measurements and Terahertz Rotational Spectrum of 12C18O

Abstract The five lowest rotational transitions of 12C180 (J =2 ← 1 to J = 6 ← 5) have been measured by saturation dip spectroscopy with an experimental accuracy of 1 to 1.5 kHz, employing phase-stabilized backward-wave oscillators. The five J rotational transitions cover the frequency range between 219 and 658 GHz. In addition, we have measured in the Doppler limited mode the rotational transitions J = 1 ← 0, J = 7 ← 6 and J = 8 ← 7. The accuracy achieved for the individual frequencies ranges between 5 and 20 kHz. Moreover the three rotational transitions J = 16 ← 15 to J = 18 ← 17 in the frequency region 1.7-2.0 THz were measured with an accuracy of 15 to 30 kHz by using the Cologne side band spectrometer for terahertz applications COSSTA.

The Submillimeter-wave Spectrum of the Formaldehyde Isotopomer H2C18O in its Ground Vibrational State

Abstract The ground state rotational spectrum of H2C18O has been studied between 485 and 835 GHz with a sample of natural isotopic composition. Additional lines have been recorded around 130 GHz and near 1.85 THz, using a recently developed far-infrared laser-sideband spectrometer. The accurate new line frequencies were fit together with previously published data to obtain greatly improved spectroscopic constants. Both Watsons S and A reduced Hamiltonians have been employed yielding the rotational constants AA = 281 961.215 (82), BA = 36 902.275 51 (36), CA = 32 513.405 89 (36), AA = 281 961.371 (82), BA = 36 904.173 32 (91), and CA = 32 511.524 65 (86) MHz, respectively.