Homepage Harold Linnartz

CRYOPAD (CRYOgenic Photoproduct Analysis Device) is an ultra-high vacuum setup fully optimized to study the effects of UV irradiation of inter- and circumstellar ice analogues. A special microwave discharge lamp is used to generate light in the deep UV, and simulating the radiation field in space. Ices are grown with monolayer precision for temperatures as low as 15 K. Reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD) are used to quantify the photodesorption, photodissociation and photoprocessing of the samples upon UV irradiation. CRYOPAD also allows to study the thermal desorption behavior of ices at very low temperatures.

In recent years it was possible with this setup to show that the photodesorption is more efficient than assumed so far in astrochemical models (explaining why some species are observed in the gas phase at temperatures where they should be accreted onto dust grains). Furthermore it was found that UV irradiation of methanol ice results in the formation of many of the complex organics that have been observed in space.

Two recent highlights:
> Formation rates of complex organics in UV irradiated CH3OH-rich ices I: Experiments; K.I. Öberg, R.T. Garrod, E.F. van Dishoeck, H. Linnartz, A&A, 504 (2009) 891.
> Photodesorption of ices II: H2O and D2O; K.I. Öberg, E.F. van Dishoeck, H. Linnartz, ApJ., 693 (2009) 1209.

SURFRESIDE (SURFace REactions SImulation DEvice) is another UHV setup that has several similarities with CRYOPAD. RAIRS and TPD are used as analytical tools to monitor reactions in the interstellar ice analogue, but chemical reactions are triggered by H-atoms that are generated in a special H-atom beam source by thermal cracking of molecular hydrogen. Currently, a second beam line is implemented that also allows to bombard the ice with O-, N-atoms, to go for more and more complicated reaction schemes.

With SURFRESIDE it has been possible to prove that methanol in space is likely formed through subsequent hydrogenation reactions of CO ice. Furthermore, H-atom addition reactions of molecular oxygen and ozone ice showed that at 15 to 20 K water can be formed on icy dust grains. The complete reaction scheme has been studied. Recently, secundary reaction products (CO2) in binary ice mixtures (CO and O2) were observed for the first time. Clearly solid state astrochemical reactions play an important role in the formation of abundant interstellar species.

Two recent highlights:
> Water formation at low temperatures by surface O2 hydrogenation I; characterization of ice penetration; S. Ioppolo, H.M. Cuppen, E.F. van Dishoeck, H. Linnartz, PCCP, 12 (2010) 12065.
>Water formation at low temperatures by surface O2 hydrogenation II; the reaction network; H.M. Cuppen, S. Ioppolo, H. Linnartz, PCCP, 12 (2010) 12077.

MATRI2CES (Mass Analyzing Tool for Reactions in Interstellar ICES) has been recently constructed and applies a MALDI-TOF detection scheme to interstellar ice analogues. The aim of the setup is to detect mass spectrometrically reaction products in an ice upon UV irradiation and/or H-atom bombardment. The ultimate goal is to repeat the famous 'Yellow stuff Greenberg experiment' but in situ and in real time. Ultimately, the setup will answer the question whether the building blocks of life can grow in the ice layers on dust grains in space.

OASIS (Optical Absorption Setup for Ice Spectroscopy) is one of the first setups, worldwide, to study chemical processes in interstellar ice analogues using optical techniques. The light of a broadband lamp is guided through an ice substrate onto a spectrometer where the light is dispersed. The technique allows to monitor chemical reactions in the ice and essentially in real time by explicitly looking at the electronic spectra of ice constituents. In the last years the focus has been on PAH containing water ice, as PAH are thought to be omnipresent in space. Gas phase studies, however, have failed in unambiguously identifying PAHs in space. As non-volatile species, PAHs are expected to freeze onto icy dust grains, and to contribute to the chemical solid state reactions. OASIS shows how these reactions depend on temperature, ice morphology and UV flux.

Two recent highlights
>Photochemistry of the PAH pyrene in water ice: the case for ion-mediated solid state astrochemistry; J. Bouwman, H.M. Cuppen, A. Bakker, L.J. Allamandola, H. Linnartz, A&A, 511 (2010) A33.
> Photochemistry of PAHs in cosmic H2O ice. Part II; Near UV/VIS spectroscopy and ionization rates; J. Bouwman, H.M. Cuppen, M. Steglich, L.J. Allamandola, H. Linnartz, A&A, in press.

SPIRAS (Supersonic Plasma InfraRed Absorption Spectrometer) is used to record high resolution infrared spectra of molecular transients of astrophysical interest. The setup comprises a planar plasma setup in which rotationally cold ions, radicals and ionic complexes are formed that are studied in direct absorption using high resolution infrared techniques. For many years a tunable diode laser has been used in combination with plasma production modulation spectroscopy to increase S/N ratios substantially.

More recently a cw OPO lasersystem has been implemented in a cavity ring-down detection scheme to further improve the detection sensitivity and particularly the accessible frequency regime. The current focus is on ionic complexes that play a role as reactive intermediates in ion-molecule gas phase reactions, such as CO-CO+ and H2-HCO+.

Two recent highlights
>Rotationally resolved infrared spectrum of the charge transfer complex [Ar-N2]+; H. Linnartz, D. Verdes, J.P. Maier, Science, 297 (2002) 1166.
>The n1 and n2 bands of Ar-HN2+; a joint theoretical/experimental study; P. Botschwina, R. Oswald, H. Linnartz, D. Verdes, J. Chem. Phys. 113 (2000) 2736.

HV SETUP is used to systematically measure solid state spectra of interstellar ice analogues in full dependence of mixing ratio and ice temperature. A recently purchased FTIR setup makes it possible to measure spectra fast and to analyze data instantaneously. The outcome is used to compare with astronomical spectra, such as from SPITZER and ISO. A recent highlight has been the detection of NH3 ice in space following the spectra recorded with this setup.

Two recent highlights:
> The c2d Spitzer spectroscopic survey of ices around low-mass young stellar objects. IV. NH3 and CH3OH; S. Bottinelli, A.C.A. Boogert, J. Bouwman, M. Beckwith, E.F. van Dishoeck, K.I. Öberg, K.M. Pontoppidan, H. Linnartz, G.A. Blake, N.J. Evans, F. Lahuis, ApJ., 718 (2010) 1100.
> Band profiles and band strengths in mixed H2O:CO ices; J. Bouwman, W. Ludwig, Z. Awad, K.I. Öberg, G.W. Fuchs, E.F. van Dishoeck, H. Linnartz, A&A 476 (2007) 995.

Our newest setup is BB-DIB, a broad band cavity enhanced spectrometer spectrometer that focuses on the identification of optical absorption features as observed through interstellar clouds.