Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

Fulvio, D.; Sivaraman, Bhalamurugan; Baratta, G. A.; Palumbo, M. E.; Mason, N.J.

doi:10.1016/j.saa.2008.12.030

Cited by 78 publications

(70 citation statements)

References 33 publications

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“…The substrate temperature can be controlled in a range between 10 and 300 K. Gas mixtures were admitted into the main chamber through a needle valve and subsequently deposited on the substrate kept at low temperature. The ice thickness is measured by means of a He-Ne laser as discussed in and Fulvio et al (2009). The ion beam current density in the ion implanter is always kept below 1 μA cm −2 to avoid macroscopic heating of the target.…”

Section: Methodsmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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Context. Solid interstellar CO 2 is an abundant component of ice dust mantles. Its ubiquity towards quiescent molecular clouds, as well as protostellar envelopes, has recently been confirmed by the IRS (InfraRed Spectrograph) aboard the Spitzer Space Telescope. Although it has been shown that CO 2 cannot be efficiently formed in the gas phase, the CO 2 surface formation pathway is still unclear. To date several CO 2 surface formation mechanisms induced by energetic (e.g., UV photolysis and cosmic ray irradiation) and nonenergetic (e.g., cold atom addition) input have been proposed. Aims. Our aim is to investigate the contribution of cosmic ray irradiation to the formation of CO 2 in different regions of the interstellar medium (ISM). To achieve this goal we compared quantitatively laboratory data with the CO 2 bending mode band profile observed towards several young stellar objects (YSOs) and a field star by the Spitzer Space Telescope. Methods. All the experiments presented here were performed at the Laboratory for Experimental Astrophysics in Catania (Italy). The interstellar relevant samples were all irradiated with fast ions (30−200 keV) and subsequently annealed in a stainless steel high vacuum chamber (P < 10 −7 mbar). Chemical and structural modifications of the ice samples were monitored by means of infrared spectroscopy. Laboratory spectra were then used to fit some thirty observational spectra.Results. A qualitative analysis shows that a good fit can be obtained with a minimum of two components. The choice of the laboratory components is based on the chemical-physical condition of each source. A quantitative analysis of the sources with known visual extinction (A V ) and methanol abundances highlights that the solid carbon dioxide can be efficiently and abundantly formed after ion irradiation of interstellar ices in all the selected YSOs in a time compatible with cloud lifetimes (3 × 10 7 years). Only in the case of field stars can the expected CO 2 column density formed upon energetic input not explain the observed abundances. This result, to be confirmed along the line of sight to different quiescent clouds, gives an indirect indication that CO 2 can also be formed in an early cloud stage through surface reactions induced by non-energetic mechanisms. In a later stage, when ices are exposed to higher UV and cosmic ray doses, the CO 2 total abundance is strongly affected by energetic formation mechanisms. Conclusions. Our results indicate that energetic processing of icy grain mantles significantly contribute to the formation of solid phase interstellar CO 2 .

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Section: Methodsmentioning

confidence: 99%

Solid CO₂in low-mass young stellar objects

Ioppolo

Sangiorgio

Baratta

et al. 2013

A&A

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“…Here we followed the same procedure described in Fulvio et al (2009). During deposition a He-Ne laser beam (λ = 543 nm) is directed towards the sample and reflected by the vacuum-sample and the sample-substrate interfaces ( Fig.…”

Section: Thickness Measurementmentioning

confidence: 99%

Formation of methyl formate after cosmic ion irradiation of icy grain mantles

Modica¹,

Palumbo²

2010

A&A

102

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Context. Methyl formate (HCOOCH 3 ) is a complex organic molecule detected in hot cores and hot corinos. Gas-phase chemistry fails to reproduce its observed abundance, which usually varies between 10 −7 and 10 −9 with respect to H 2 . Aims. Laboratory experiments were performed in order to investigate a solid-state route of methyl formate formation, to obtain an estimate of the amount that can be formed, and to verify whether it can account for the observed abundances. Methods. Several solid samples (16 K) of astrophysical interest were analyzed by infrared spectroscopy in the 4400−400 cm −1 range. The infrared spectral characteristics of frozen methyl formate were studied by deriving their band strength values. The effects produced upon warm-up of the samples were analyzed comparing the spectra taken at different temperatures. In order to study the formation and destruction mechanism of methyl formate in the interstellar ices, a binary mixture of methanol (CH 3 OH) and carbon monoxide (CO) ice and a sample of pure methanol were irradiated at 16 K with 200 keV protons. Methyl formate was identified through its fundamental mode (CH 3 rocking) at about 1160 cm −1 . Results. We present the mid-infrared methyl formate ice spectrum showing both the amorphous (16 K) and the crystalline (110 K) structure. We report novel measurements of the band strength values of the six main methyl formate bands. We prove the formation and the destruction of methyl formate after irradiation of CH 3 OH and a CO:CH 3 OH mixture. Extrapolating our results to the interstellar medium conditions we found that the production timescale of methyl formate agrees well with the evolutionary time of molecular clouds. The comparison with the observational data indicates that the amount of methyl formate formed after irradiation can account for the observed abundances. Conclusions. The present results allow us to suggest that gas phase methyl formate observed in dense molecular clouds is formed in the solid state after cosmic ion irradiation of icy grain mantles containing CO and CH 3 OH and released to the gas phase after desorption of icy mantles.

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“…This correction takes into account the longer path length of the IR beam at an incidence angle θ i = 45 deg (Fulvio et al 2009;Modica & Palumbo 2010).…”

Section: Experimental Apparatus and Proceduresmentioning

confidence: 99%

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

Garozzo

Rosa

Kaňuchová

et al. 2011

A&A

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Context. Infrared observations show the presence of icy mantles along the line of sight toward young stellar objects (YSOs), where a temperature gradient is expected and indirectly observed. In this environment, icy mantles are affected by ion and UV irradiation. Laboratory experiments show that molecules are formed after irradiation of icy mixtures. However, most of the experiments done so far have been performed in the temperatures range of 10-20 K. Aims. To extend previous work we irradiated some icy mixtures, namely H 2 O:CO=10:1, H 2 O:CH 4 =4:1, and H 2 O:CO 2 =3:1 at two different temperatures (12 K and 40 or 60 K) to study the effects of temperature on the synthesis of molecules and the decrease in their parent species after ion irradiation. Methods. The experiments were performed in a high-vacuum chamber (P < 10 −7 mbar), where icy samples were irradiated with 30 keV He + ions and analyzed by a FTIR spectrophotometer. Infrared spectra of the samples were recorded after various steps of irradiation. Results. We found that the temperature affects the behavior of the volatile species (i.e., CO and CH 4 ) during irradiation. As a consequence, the production of molecular species is generally more prevalent at 12 K than at either 40 or 60 K, while the decrease in their parent volatile species is faster at high temperature. Conclusions. We conclude that the behavior of each species depends on the value of its sublimation temperature with respect to the temperature of the sample. If this latter is higher than the sublimation temperature of a given species, then the effects of thermal desorption compete with those due to irradiation.

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Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

Cited by 78 publications

References 33 publications

Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects

Formation of methyl formate after cosmic ion irradiation of icy grain mantles

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

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Novel measurements of refractive index, density and mid-infrared integrated band strengths for solid O2, N2O and NO2:N2O4 mixtures

Cited by 78 publications

References 33 publications

Solid CO2in low-mass young stellar objects

Solid CO2in low-mass young stellar objects

Formation of methyl formate after cosmic ion irradiation of icy grain mantles

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

Contact Info

Product

Resources

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Solid CO₂in low-mass young stellar objects

Solid CO₂in low-mass young stellar objects