CAS@MPE Laboratories

Nearly 200 molecules have been detected in extraterrestrial environments. Due to the extreme nature of many such environments compared to those on Earth, many of these species are difficult to prepare and observe, and require only specific conditions that only a laboratory can provide: specific temperatures ranges, specific pressures, specific non-thermal excitations, specific reactants, or any combination of the aforementioned. At the Centre for Astrochemical Studies we investigate the millimetre/sub-millimetre spectra of such molecules in the laboratory, with the aim of providing improved spectral data to guide the astronomical searches and to assist the interpretation of the observations. One particular interest focuses on light molecular ions and radicals. more

The cryogenic laboratory developed at the CAS group is dedicated to the study of optical and spectroscopic properties of interstellar ice analogs (CASICE). The chemical and physical processes occurring in icy mantles, which cover dust grains in many astronomical environments, are of key importance to unravel the molecular complexity observed in space. These processes are critically affected by the ice composition and structure, and therefore it is necessary to develop a reliable methodology to identify imprints of different ices in observable properties of cosmic dust. more

In some cases within the interstellar medium, it is important to understand the low-temperature cooling of molecules not by purely radiative processes, which are relatively well-understood and well-modeled, but also by state-selective gas-phase collisions. In some cases, this can be modeled in a purely theoretical way, however, it remains a significant challenge for most systems and even impossible in some cases. It is thus important that laboratory experiments are used to either verify theory for challenging cases, or to provide the sole source of data for the impossible cases. At CAS we follow two approaches to study collisions: (1) Analysis of line profiles. (2) Observation of population transfer by time-resolved pump-probe experiements. more

CASAC is a long-pathlength absorption spectrometer. The centerpiece of this spectrometer is a long-pathlength glass tube (3m-long x 5cm-diameter), which serves as the main flow cell. In the center is a region 2 meters in length, which has a large metal electrode at each end, wrapped with tubing on the outside of the cell, and is centered in a copper solenoid, enabling the ability to form a cooled, confined plasma from an appropriate mixture of gaseous precursors. Spectroscopy through the cell can then be performed in the range of 80–1100 GHz using Schottky-based multiplier chains (AMC, Virginia Diodes Inc.) and either Schottky detectors (VDI) or a hot-electron bolometer (QMC Instruments) for detection. Optionally, a wire-grid polarizer and retroreflector can be used to perform double-pass spectroscopy, which can help with saturation spectroscopy (i.e. Lamb Dip). more

To extend the capabilities of the CAS laboratory for rotational spectroscopy a free-jet supersonic expansion experiment for probing low-temperature, unstable molecules has been developed. The instrument operates in the 80–1600 GHz range (4–0.2 mm) and can be combined with the CPFTS. The molecular beam, a gas generated by the mixture of different chemical samples connected to mass flow controllers, is injected into a high-vacuum expansion chamber (~10-5 Torr / 10-3 bar) through a 1-mm pinhole of a pulsed valve. The supersonic expansion allows the adiabatic cooling of the molecular beam, yielding temperatures in the range of approximately 7 to 20 K, depending on the buffer gas used, significantly lower than those reachable in the CASAC spectrometer (~ 80 K). The coupling of the molecular beam to the mm- and submm-wave radiation is obtained through a roof-top mirror placed inside the chamber, which also contains the aperture through which the molecular sample is injected. The production of unstable species is achieved by attaching a high-voltage low-current DC nozzle to the front of the valve, through which the molecules pass right after the pulsed valve and prior to free expansion. more

A broadband Chirped-Pulse Fourier Transform Spectrometer (CP-FTS) is set up in the CAS laboratories covering the  frequency range of 6–26 GHz, with an instantaneous bandwidth of 7 GHz and frequencies in the range of 75–110 GHz with a bandwidth of about 20 GHz with high resolution.
The electronics are situated in a movable rack, so that it can be most easily coupled to a variety of chambers/cells, depending on the desired sample to study, e.g. a 1.5 m- waveguide or the molecular jet apparatus. more

The CAS laboratory is home to a THz Time-Domain Spectrometer (TDS1008, BATOP). The TDS uses an ultrafast laser (λ=785 nm, Δt_pulse=100 fs) which provides, in combination with high-performance photo-conductive antennas, a large spectral bandwidth (0.05–5 THz) and a high dynamic range in signal. It is capable of pulse pump-probe delays up to 650 ps, and is thus compatible with a wide range of optically-active samples. The instrument has built-in mounts for small samples, and it can also be interfaced to a closed cycle, ultra-low vibration cryostat (CS210SFg-GMX, Advanced Research Systems). more

The high-resolution, broadband Fourier transform infrared spectrometer (IFS 120HR, Bruker) is equipped with a number of radiation sources and detectors, providing access to infrared wavelengths in the range of 2–350 μm at a resolution of 0.001 cm^-1. The spectrometer uses either dedicated cells for gaseous molecular samples or can be combined with a cryostat to record spectra of ice analogs. more

The CAS cryogenic ion trap is a versatile tool that extends CAS laboratory domain to ion-molecule interaction at cold temperatures. Closed cycle cryostat allows us to reach temperatures lower than 4 K for the neutral buffer gas. The radio frequency 22 pole ion trap assures very well defined trapping and cooling conditions for the ions from the lightest ion H+ (mass 1) up to several hundred mass units. Differential pumping and complete separation of fore-vacuum of the ion source and the interaction regions allows studies with minimal influence of the ion precursor gas to the ion-neutral of choice interactions. more

A Raman Imaging Microscope (alpha300 R, WITec) is installed in the CAS laboratory. The instrument is equipped with two lasers operating at 488 and 785 nm, and two spectrometers with a resolution of 1 cm^-1. The lateral resolution of the microscope can reach the submicron level in the most favorable configuration. Microspectroscopy is the primary technique to analyze spectroscopic properties in 2D and 3D space, enabling the study of composite materials. With this technique it is thus possible to examine samples like meteorites and interstellar dust, and to assess the role of different substrates in the interaction with the ice mantles. The Raman microscope is coupled with a customized design cryostat, configured with a tunable gas inlet capable of depositing spatially resolved ice samples to address their surface diffusion properties. more