CAS@MPE Laboratories

Research Topics

Molecular Spectroscopy of Reactive Species
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
Optical Characterization of Interstellar Ice Analogues
The cryogenic laboratory developed at the CAS group has reached the operative stage with the publication of the first paper about IR spectroscopy of water and oxygen ice mixtures. The experimental work has been extended to the measurement of the optical constant in the THz regime of CO ice to estimate the dust opacity in dense and cold regions of pre-stellar cores and protoplanetary disks. New projects are under development, regarding the Raman spectroscopy and imaging of ice analogs. more
Molecular Collisional Dynamics
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

Instruments

The CASAC (<span style="text-decoration: underline;">CAS</span> <span style="text-decoration: underline;">A</span>bsorption <span style="text-decoration: underline;">C</span>ell) Experiment
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
CASJET (The Molecular Jet Experiment)
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
The CP-FTS (<span style="text-decoration: underline;">C</span>hirped <span style="text-decoration: underline;">P</span>ulse <span style="text-decoration: underline;">F</span>ourier <span style="text-decoration: underline;">T</span>ransform <span style="text-decoration: underline;">S</span>pectrometer)
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
CASICE (The Ice Experiment)
The CAS laboratories is home to a THz Time-Domain Spectrometer (TDS1008, BATOP). The TDS uses an ultrafast laser (λ=785 nm, Δtpulse=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 (4 orders of magnitude) 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 FTIR (<span style="text-decoration: underline;">F</span>ourier <span style="text-decoration: underline;">T</span>ransform <span style="text-decoration: underline;">I</span>nfra<span style="text-decoration: underline;">R</span>ed Spectrometer)
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 the ice cryostat to record spectra of ices. more
CASTRAP (Cryogenic Ion Trap)

CASTRAP (Cryogenic Ion Trap)

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.
Go to Editor View