Laser desorption time-of-flight mass spectrometry of ultraviolet photo-processed ices

Bossa

Linnartz

2016

A&A

Self Cite

Context. Methanol in the interstellar medium mainly forms upon sequential hydrogenation of solid CO. With typical abundances of up to 15% (with respect to water) it is an important constituent of interstellar ices where it is considered as a precursor in the formation of large and complex organic molecules (COMs), e.g. upon vacuum UV (VUV) photo-processing or exposure to cosmic rays. Aims. This study aims at detecting novel complex organic molecules formed during the VUV photo-processing of methanol ice in the laboratory using a technique more sensitive than regular surface diagnostic tools. In addition, the formation kinetics of the main photo-products of methanol are unravelled for an astronomically relevant temperature (20 K) and radiation dose. Methods. The VUV photo-processing of CH 3 OH ice is studied by applying laser desorption post-ionisation time-of-flight mass spectrometry (LDPI TOF-MS), and analysed by combining molecule-specific fragmentation and desorption features. Results. The mass spectra correspond to fragment ions originating from a number of previously recorded molecules and from new COMs, such as the series (CO) x H + y , with x = 3 and y < 3x − 1, to which prebiotic glycerin belongs. The formation of these large COMs has not been reported in earlier photolysis studies and suggests that such complex species may form in the solid state under interstellar conditions.

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Fittingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Laser desorption time-of-flight mass spectrometry of vacuum UV photo-processed methanol ice

Bossa

Linnartz

2016

A&A

Self Cite

“…The experiments have been carried out in our ultra-high vacuum (UHV) set-up MATRI 2 CES, described in detail in a previous publication (Paardekooper et al 2014). Briefly, MATRI 2 CES consists of two different UHV chambers, a main chamber and a time-of-flight chamber.…”

Section: Experimental Set-upmentioning

confidence: 99%

A novel approach to measure photodesorption rates of interstellar ice analogues

Fedoseev

Riedo

et al. 2016

A&A

Self Cite

Context. In recent years photodesorption rates have been determined in dedicated laboratory experiments for a number of different interstellar ice analogues. These rates are important in order to model non-thermal desorption processes that, for example, affect gas-phase abundances of species and determine the position of photo-induced snow lines in protoplanetary disks. However, different groups using similar experiments have found significant deviating photodesorption values. Aims. Here a new measurement concept is introduced that allows photodesorption rates to be determined following a different experimental approach. The potential of this method is demonstrated using the example of pure CO ice, the solid that gives the most striking discrepancies in the published results. Methods. The new experimental approach uses laser desorption post-ionisation time-of-flight mass spectrometry. It is based on the concept that the physical and geometrical properties of the plume obtained by laser induced desorption of the ice directly depend on the original ice thickness. This allows the ice loss to be determined as function of vacuum ultraviolet (VUV) fluence, which results in a photodesorption rate. The method has the additional advantage that it records all ice species, including photoproducts generated by the VUV irradiation. As a consequence, the method introduced here is also suited to determine the overall photodesorption rate of mixed ices. Results. The photodesorption rate for CO ice at 20 K has been determined as (1.4 ± 0.7) × 10 −3 molecules per incident VUV photon. This result is compared to existing experimental and theoretical values and the astronomical relevance is discussed.

Towards disentangling photodesorption and photodissociation in astronomical ice analogues

Bulak¹,

Bouwman³

et al. 2019

Proc. IAU

UV irradiation of ices plays an important role in different inter- and circumstellar environments. Following the absorption of UV photons in ice, two processes compete: photodesorption and photodissociation/chemistry. From an experimental point of view it is very hard to discriminate between photodesorption and photodissociation (and resulting photochemistry). In this work we present our first attempts to distinguish both effects. The performance is demonstrated on the example of CO-ice, known not to dissociate upon UV irradiation, and CH4-ice that does fragment.