Photolytic behaviour of methane at Lyman-α and 248nm: Studies in the frame of a simulation program of Titan’s atmosphere (S.E.T.U.P.)

Romanzin, C.; Bénilan, Y.; Jolly, A.; Gazeau, M.‐C.

doi:10.1016/j.asr.2008.04.011

Cited by 14 publications

(8 citation statements)

References 38 publications

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“…CH 4 and CO are small molecules with a simple photodissociation chemistry: CH 4 mainly loses an H to form CH 3 , though direct dissociation to CH 2 is also possible (Romanzin et al 2008), while CO does not photodissociate measurably with the UV lamp in this experiment ( Öberg et al 2007).…”

Section: Dependence Of Complex Chemistry On Experimental Variablesmentioning

confidence: 89%

Formation rates of complex organics in UV irradiated CH₃OH-rich ices

Öberg¹,

Garrod²,

Dishoeck

et al. 2009

A&A

434

342

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Context. Gas-phase complex organic molecules are commonly detected in the warm inner regions of protostellar envelopes, so-called hot cores. Recent models show that photochemistry in ices followed by desorption may explain the observed abundances. There is, however, a general lack of quantitative data on UV-induced complex chemistry in ices. Aims. This study aims to experimentally quantify the UV-induced production rates of complex organics in CH 3 OH-rich ices under a variety of astrophysically relevant conditions. Methods. The ices are irradiated with a broad-band UV hydrogen microwave-discharge lamp under ultra-high vacuum conditions, at 20-70 K, and then heated to 200 K. The reaction products are identified by reflection-absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD), through comparison with RAIRS and TPD curves of pure complex species, and through the observed effects of isotopic substitution and enhancement of specific functional groups, such as CH 3 , in the ice. Results. Complex organics are readily formed in all experiments, both during irradiation and during the slow warm-up of the ices after the UV lamp is turned off. The relative abundances of photoproducts depend on the UV fluence, the ice temperature, and whether pure CH 3 OH ice or CH 3 OH:CH 4 /CO ice mixtures are used. C 2 H 6 , CH 3 CHO, CH 3 CH 2 OH, CH 3 OCH 3 , HCOOCH 3 , HOCH 2 CHO and (CH 2 OH) 2 are all detected in at least one experiment. Varying the ice thickness and the UV flux does not affect the chemistry. The derived product-formation yields and their dependences on different experimental parameters, such as the initial ice composition, are used to estimate the CH 3 OH photodissociation branching ratios in ice and the relative diffusion barriers of the formed radicals. At 20 K, the pure CH 3 OH photodesorption yield is 2.1(±1.0) × 10 −3 per incident UV photon, the photo-destruction cross section 2.6(±0.9) × 10 −18 cm 2 . Conclusions. Photochemistry in CH 3 OH ices is efficient enough to explain the observed abundances of complex organics around protostars. Some complex molecules, such as CH 3 CH 2 OH and CH 3 OCH 3 , form with a constant ratio in our ices and this can can be used to test whether complex gas-phase molecules in astrophysical settings have an ice-photochemistry origin. Other molecular ratios, e.g. HCO-bearing molecules versus (CH 2 OH) 2 , depend on the initial ice composition and temperature and can thus be used to investigate when and where complex ice molecules form.

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Section: Dependence Of Complex Chemistry On Experimental Variablesmentioning

confidence: 89%

Formation rates of complex organics in UV irradiated CH₃OH-rich ices

Öberg¹,

Garrod²,

Dishoeck

et al. 2009

A&A

434

342

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“…Typical leak tight windows made of LiF, CaF 2 , or MgF 2 are capable of handling the pressure difference between the ultrahigh vacuum of the beamline and the pressure of the reactor but are opaque below~110 nm (11.3 eV), preventing the activation of molecular nitrogen. Photochemical reactors operating at Ly alpha and above therefore focus on methane chemistry [Ádámkovics and Boering, 2003;Romanzin et al, 2008;Trainer et al, 2004]. Although it is relatively easy to irradiate any media with UV photons through windows, it is much more difficult to deliver to a gas sample VUV photons with energy above the transparency limit of the windows.…”

Section: Introductionmentioning

confidence: 99%

Titan's atmosphere simulation experiment using continuum UV‐VUV synchrotron radiation

et al. 2013

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[1] A new reactor, named APSIS for Atmospheric Photochemistry Simulated by Synchrotron, is designed for simulating the reactivity occurring in planetary upper atmospheres. In this reactor, a gas mixture roughly reproducing Titan's main atmosphere composition (N 2 /CH 4 = 90/10) is irradiated by a continuous spectrum in the 60À350 nm range, provided by the DISCO beamline at the SOLEIL synchrotron radiation facility. This spectral range enables the dissociation and ionization of N 2 and CH 4 , as observed in plasma reactors and Titan's ionosphere. The neutral products are detected in situ by quadrupole mass spectrometry and collected with a cryogenic trap for ex situ analysis by gas chromatography-mass spectrometry. The detected reaction products include C2, C3, C4, and probably C5 organic compounds, with important amounts of nitrogen-bearing species: HCN, CH 3 CN, and C 2 N 2 . Neutral mass spectra obtained with APSIS are compared with Ion and Neutral Mass Spectrometer experiments of the Cassini space probe in the upper Titan atmosphere and with other results of current Titan atmosphere chemistry laboratory simulations.

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“…This rather stable molecule is therefore photoionized and dissociated also at rather high altitudes. The photoproducts from methane with Lyman-α radiations have been well established experimentally 28,29 , with fragment quantum yields Φ i :…”

Section: 1 3 Photolysis From the Upper Atmosphere Down To The Surfacementioning

confidence: 99%

CHAPTER 4. Unveiling Early Earth Photochemistry Through Experimental Simulations of Planetary Atmospheres

Carrasco¹,

Gautier²

2021

Comprehensive Series in Photochemical &Amp; Photobiological Sciences

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This chapter summarizes the contributions of the early Earth atmosphere between late Hadean and early Archean eons (4.3 to 3.7 Ga) to sustain the emergence of life: influencing both the climate and prebiotic chemical synthesis through photochemistry. Almost no geological constraints remain on these early ages so that chemical scenarios are largely explored through experimental simulation. Main scientific results through time are given, from the pioneer experiment by Miller and Urey in the 50's, up to the most recent studies focusing on high altitude photochemistry.

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Photolytic behaviour of methane at Lyman-α and 248nm: Studies in the frame of a simulation program of Titan’s atmosphere (S.E.T.U.P.)

Cited by 14 publications

References 38 publications

Formation rates of complex organics in UV irradiated CH₃OH-rich ices

Formation rates of complex organics in UV irradiated CH₃OH-rich ices

Titan's atmosphere simulation experiment using continuum UV‐VUV synchrotron radiation

CHAPTER 4. Unveiling Early Earth Photochemistry Through Experimental Simulations of Planetary Atmospheres

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Photolytic behaviour of methane at Lyman-α and 248nm: Studies in the frame of a simulation program of Titan’s atmosphere (S.E.T.U.P.)

Cited by 14 publications

References 38 publications

Formation rates of complex organics in UV irradiated CH3OH-rich ices

Formation rates of complex organics in UV irradiated CH3OH-rich ices

Titan's atmosphere simulation experiment using continuum UV‐VUV synchrotron radiation

CHAPTER 4. Unveiling Early Earth Photochemistry Through Experimental Simulations of Planetary Atmospheres

Contact Info

Product

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Formation rates of complex organics in UV irradiated CH₃OH-rich ices

Formation rates of complex organics in UV irradiated CH₃OH-rich ices