Gallery

The final steps in one of the multiple dissociation pathways of a polycyclic aromatic hydrocarbon cation: 1-ethynylpyrene+ (atomic bonds are not rendered according to their type and are only a visual aid). Animation based on calculations I ran for the study Threshold dissociation of the 1-ethynylpyrene cation at internal energies relevant to H I regions (DOI, arXiv)

My pet instrument in the Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena: pulsed, supersonic gas expansion chamber and laser source for the spectroscopy of cold, collision-free molecules. Spectroscopy techniques: cavity ring-down laser absorption, laser-induced fluorescence, dispersed laser-induced emission, and cavity ring-down laser-induced fluorescence.

Partial view of the program I designed with LabVIEW for the cavity ring-down laser absorption spectrometer I set up in Jena; it controls the tunable dye laser advance, and acquires and treats data imported from a digital oscilloscope and a gated integrator.

View of the front panel of the control and acquisition program of the cavity ring-down laser absorption spectrometer during a test. The loss coefficient spectrum of the cavity open to air is displayed in the top panel revealing a well resolved rotational structure of the b-X (2-0) band of 16O2. The scan was performed without wavelength calibration for which two supplementary acquisition channels can be used.

Example of absorption band detection at low resolution with laser-induced fluorescence: jet-cooled tetracene. The horizontal scale is calibrated by measuring Ne I lines simultaneously (not shown). Comparison with a measurement by van Herpen et al. (1987): agreement!

Test of the dispersed emission spectrometer I added to the supersonic gas expansion set up in Jena: jet-cooled fluorene. Comparison with a measurement by Saigusa & Lim (1991).

An example of simultaneous cavity ring-down laser absorption (CRDS-A) and cavity ring-down laser-induced fluorescence (CRDS-F) measurements: jet-cooled naphthalene. The spectra are different because the two techniques probe different volumes: CRDS-A probes the whole  diameter of the supersonic expansion (and actually the whole length of the optical cavity) whereas CRDS-F probes the center of the expansion, for the collecting optics enable a point-like spatial resolution . The horizontal scale is calibrated by measuring Ne I lines simultaneously (one shown).

Absorption spectrum of molecules isolated in a neon matrix, with site effect: perylenetetracarboxylic dianhydride (PTCDA). Comparison with a measurement by Dvorak et al. (2012).

Absorption spectrum of atoms isolated in a neon matrix: iron (Fe). Comparison with a synthetic spectrum computed using NIST's Atomic Spectra Database: note the blue shift!

Can I fit temperature programmed desorption (TPD) curves?  Here is the example of CO molecules on an MgO(100) surface with a coverage of 0.71 with measured curve adapted from Fig. 3 in Dohnálek et al. (2001) assuming 1015 molecules per monolayer.  The fitted curve supposes a coverage-dependent binding energy, model described by Eq. 3 in He et al. (2016). I chose it arbitrarily for this demonstration and do not claim it is the best choice for this system. Note that the fitted N0 value corresponds to a coverage of 0.48 instead of 0.71 because only the first desorption peak is taken into account in this test. Two parameters out of six were fixed in order to obtain a converging fitting and reasonable errors.

Testing a quartz crystal microbalance (QCM) cooled to 14 K with a compressed-He, closed-cycle cryocooler (temperature limited by the presence of an 800 K-capable heating element).  The QCM is exposed to a flux of C atoms during 121 minutes, its temperature increasing because of the heat radiated by the C source (Krasnokutski & Huisken 2014). Decreasing frequency at the QCM is consistent with material deposition. The thickness of the deposited carbon layer is estimated at 6 to 10 nm.

Potassium bromide (KBr) is the material of substrates for mid-infrared (MIR) transmission or absorption spectroscopy. Whenever I need a half disk –it happens routinely–, I break a full one by taking advantage of the crystalline structure.

Common source of vacuum ultraviolet (VUV) photons, the microwave-discharge hydrogen-flow lamp. Atoms, molecules, and grains present in the interstellar medium are exposed to VUV photons emitted by stars. Here the lamp is used to study the response of grains to VUV exposure.

I was asked in the past to set up –fast– a source of oxygen atoms for a visiting student. The simplest solution was to equip the microwave-discharge hydrogen-flow lamp (see above) with an accessory. Et voilà! This source has yet to be fully characterized, though. Note that the colors of the hydrogen and oxygen plasmas differ.