r0pt Figure Since twenty years photonics-based terahertz (THz) sources have made great progress. They are now usable for low- and high-resolution molecular spectroscopy in the 0.1-4 THz range (3-130 cm⁻¹). We will present the principles of near-infrared laser-based THz set-ups: time-domain spectroscopy (see figure showing ambient pressure H₂O lines) and frequency-domain photomixing. Then we will review the different types of high bandwidth semiconductors photodetectors used to convert laser beams into THz beams. Two families are mainly used: photoconductors and photodiodes. Advantages and drawbacks of each will be presented. The subject of THz antennas will be also discussed and a state of the art will be given including the devices developed at IEMN. Some example of molecular spectroscopy measurements using these devices at various frequencies and resolutions will be given. Finally new ways for photonics-based THz sources will be exposed.

The goal of our project is to develop a new high-resolution spectrometer on the AILES beamline of synchrotron SOLEIL. The spectrometer will record absorption spectra in the 1-5 THz range with sub-MHz resolution using a heterodyne detection scheme. We recently performed a test experiment using the far-IR continuum produced by synchrotron radiation in the multibunch mode, a multiplication chain as local oscillator, and a hot electron bolometer (HEB) as heterodyne mixer. The set-up allowed the detection of one D₂O absorption line centered at about 782 GHz (^RQ(4)_0,4) with a resolution better than 1 MHz. We will present the details of the experiment and some instrumental developments in progress.

Transition metal organometallic complexes are known for their catalytic activation of small molecules. For example, CO₂ activation by Ni¹⁺(cyclam) complexes has recently been reported in the gas-phaseF. S. Menges, S. M. Craig, N. Tötsch, A. Bloomfield, S. Ghosh, H. J. Krüger and M. A. Johnson, Angewandte Chemie International Edition, 2016, 55, 1282-1285. where the oxidation state of the metal appeared to be the key for the electrochemical reduction of CO₂. In this contribution, we show that metal(II) complexes, including Ni-cyclam, generated via electrospray ionization can be charge reduced inside a quadrupole ion trap mass spectrometerJ. Martens, G. Berden, C. R. Gebhardt and J. Oomens, Review of Scientific Instruments, 2016, 87, 103108.QIT MS) via an electron transfer reduction (ETR) reaction using fluoranthene radical anions as reagentsM. U. Munshi, S. M. Craig, G. Berden, J. Martens, A. F. DeBlase, D. J. Foreman, S. A. McLuckey, J. Oomens and M. A. Johnson, The Journal of Physical Chemistry Letters, 2017, 8, 5047-5052 Moreover, their IR spectra can be recorded by action spectroscopy using the FELIX free electron laser, which enables their structural characterization. The complex in either of two charge states is isolated by its m/z, stored and irradiated with tunable IR light in the range of 500-1800 cm⁻¹. IR induced dissociation occurs upon resonant vibrational excitation of the trapped ions, so that an IR spectrum of the (charge reduced) complexes can be obtained by plotting the dissociation yield as a function of IR laser frequency. Experimental spectra are compared with theoretical spectra computed at the density functional theory (DFT) level to obtain detailed structural information of the complexes undergoing charge reduction, eventually providing new insights in their catalytic capabilities. F. S. Menges, S. M. Craig, N. Tötsch, A. Bloomfield, S. Ghosh, H. J. Krüger and M. A. Johnson, Angewandte Chemie International Edition, 2016, 55, 1282-1285., J. Martens, G. Berden, C. R. Gebhardt and J. Oomens, Review of Scientific Instruments, 2016, 87, 103108.( M. U. Munshi, S. M. Craig, G. Berden, J. Martens, A. F. DeBlase, D. J. Foreman, S. A. McLuckey, J. Oomens and M. A. Johnson, The Journal of Physical Chemistry Letters, 2017, 8, 5047-5052.

Inversion of population in the terahertz (THz) range can be obtained thanks to the optical pumping of polar molecules in the mid-infrared range. Generally it is done with CO₂ lasers but recently we have demonstrated the first molecular laser pumped by a quantum cascade laser (QCL). It is based on the optical pumping of the NH₃ molecule in the ν₂=1 state. The gain is obtained by the stimulated emission on pure inversion transitions of NH₃ (large amplitude motions) around 1 THz that are not accessible to continuous-wave (CW) CO₂ lasers. We present here CW high-resolution gain measurements of two strong lines: the (3,3) around 1.073 THz and the (4,4) around 1.083 THz. The measurements are done with a THz multiplication chain and an InSb bolometer. The gain profiles are recorded at different pressure and different QCL frequencies as for an IR/THz double resonance experiment. The highest gain at the best conditions are obtained with the (3,3) line: 10 dB/m for a pump power of about 40 mW. To our knowledge this gain is highest measured in the THz range for a CW-pumped molecule. These measurements will help the understanding and the design of our NH₃ lasers. This kind of laser will find applications in THz molecular spectroscopy/astronomy as a source or as a local oscillator for heterodyne detection.

DL-Norvaline is a molecular crystal at room temperature and it undergoes a phase transition when cooled below 190 K. This phase transition is believed to be Martensitic. We investigate this phase transition by measuring its terahertz (THz) spectrum over a range of temperatures. Temperature-dependent THz time-domain spectroscopy (THz-TDS) measurements reveal that the transition temperature (T_{β→ α}) is 190 K. The influence of nucleation seeds was analyzed by determining the T_{β→ α} of molecular crystals with varying grain size. Grains of 5 μm or less result in a lower transition temperature (T_{β→ α} = 180 K) compared to larger grains of 125–250 μm (T_{β→ α} = 190 K). Additionally, we gain insight into the physical process of the phase transition via temperature-dependent THz-TDS spectra of doped and mixed molecular crystals. The addition of molecular dopants, which differ from DL-norvaline only at the end of the side chain which resides in the hydrophobic layers of the crystal, decreases T_{β→ α}. This is consistent with a solid-solid phase transition in which the unit cell shifts along this hydrophobic layer, and it leads us to believe that the phase transition in DL-norvaline is Martensitic in nature.

l0pt Figure Cavity enhanced pure rotational spectroscopy has long been a potent laboratory tool for the elucidation of structure and dynamics in isolated molecular systems where sensitive pulsed-echo techniques are routinely performed up to frequencies as high  ∼ 50 GHz. Although the associated narrow linewidths ( ∼ 800kHz), wide-bandwidth (often > 10 GHz), and long optical path lengths have long been identified as a desirable combination for sensitive and specific gas sensing, the unaccommodating size and power requirements of traditional microwave optics/electronics are unsuitable for the stringent demands required for in situ deployment. Additionally, efforts to drive pulsed-echo techniques into millimeter and submillimeter wavelength regimes, where the size of optics can be reduced without suffering large diffraction losses, have failed largely due to inefficiencies of injecting radiation into the resonant optical cavity. Recent pursuits at the Jet Propulsion Laboratory to realize compact, low-power devices capable of in situ chemical detections on extra-terrestrial objects have found success in calling upon novel transmitter and receiver elements built from CMOS architectures commonly employed in the high-speed communications industry. These low-power integrated circuit chipsets can be embedded directly into quasi-optical devices allowing for the realization of cavity based instruments where all source and detection electronics are hosted by a single 16 in² printed circuit board. The current talk will present a full system description of this miniaturized CMOS-based pulse-echo rotational spectrometer,D. J. Nemchick et al., "A 90-102 GHz CMOS Based Pulsed-Echo Fourier Transform Spectrometer: New Approaches for In Situ Chemical Detection and Millimeter-Wave Cavity-Based Molecular Spectroscopy," Rev. Sci. Inst., In Submission.hich has an operational bandwidth of 90-105 GHz, along with experimental trials taken in bulk gas flows and seeded molecular beam environments.

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D. J. Nemchick et al., "A 90-102 GHz CMOS Based Pulsed-Echo Fourier Transform Spectrometer: New Approaches for In Situ Chemical Detection and Millimeter-Wave Cavity-Based Molecular Spectroscopy," Rev. Sci. Inst., In Submission.w

Direct digital synthesizers (DDS) have a number of advantages, especially such as the high precision and rate of frequency adjustment. In addition, these synthesizers possess a unique property to allow changing the frequency from one value to another with continuous phase. Few years ago, we built fast-scan absorption spectrometer with Schottky diode frequency multiplication chains as a radiation source.A. Pienkina, R.A. Motiyenko, L. Margulès et al. ISMS, 71st symposium (2016), FB05he rapid frequency scan in the spectrometer is provided by RF synthesizer based on up-conversion of the DDS signal. Owing to the capability of fast frequency switching, the same up-converted RF synthesizer may generate short pulses to polarize molecules and subsequently may be used as a local oscillator in the heterodyne detection of free induction decay. This feature simplifies the spectrometer design, as it allows using only one radiation source to polarize molecular sample, and to detect molecular signal. Using this principle, we built a Fourier transform spectrometer in the millimeter wave range. The spectrometer covers the frequency range between 150 and 220 GHz. In the current design, the RF synthesizer allows generation of frequency pulses with a bandwidth inverse proportional to pulse duration, as well as chirped pulses with a bandwidth of about 350 MHz. The performances of the spectrometer will be presented and discussed.

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A. Pienkina, R.A. Motiyenko, L. Margulès et al. ISMS, 71st symposium (2016), FB05T

Methanethiol, CH₃SH, has been found in the warm and dense parts of high as well as low mass star-forming regions.See, e.g., H. S. P. Müller at al., Astron. Astrophys. 587 (2016) A92; M. N. Drozdovskaya et al., Mon. Not. R. Astron. Soc., accepted, arXiv: 1802.02977; and references therein.he molecule is also of fundamental interest because of the large amplitude internal rotation of the CH₃ group whose effects are somewhat less pronounced than in its lighter homolog CH₃OH. In the course of our ongoing study of CH₃³²SH,V. Ilyushin et al., TI04 at the 72nd ISMS, 2017e have recorded new spectra which currently cover 49−510 GHz.The work in Kharkov was done under support of the Volkswagen foundation. The assistance of the Science and Technology Center in the Ukraine is acknowledged (STCU partner project #P686). The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via grant SFB 956, project B3 and via the Gerätezentrum "Cologne Center for Terahertz Spectroscopy".hese spectra, as well as existing ones covering part of the 1.1−1.5 THz region,L.-H. Xu at al., J. Chem. Phys. 137 (2012) 104313.ere inspected for lines of CH₃³⁴SH. We made extensive assignments of ∆K = 0 transitions in v_t = 0 to 2. Numerous assignments of ∆K = ±1 transitions were made in v_t = 0 and to a lesser extent in the two higher torsional states. We will present results of modeling these data with the RAM36 program and of searches for this isotopolog in our 3 mm ALMA data of Sagittarius B2(N).

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See, e.g., H. S. P. Müller at al., Astron. Astrophys. 587 (2016) A92; M. N. Drozdovskaya et al., Mon. Not. R. Astron. Soc., accepted, arXiv: 1802.02977; and references therein.T V. Ilyushin et al., TI04 at the 72nd ISMS, 2017w The work in Kharkov was done under support of the Volkswagen foundation. The assistance of the Science and Technology Center in the Ukraine is acknowledged (STCU partner project #P686). The work in Cologne was supported by the Deutsche Forschungsgemeinschaft (DFG) via grant SFB 956, project B3 and via the Gerätezentrum "Cologne Center for Terahertz Spectroscopy".T L.-H. Xu at al., J. Chem. Phys. 137 (2012) 104313.w