The Refractive Index of Amorphous and Crystalline Water Ice in the UV–vis

Kofman, Vincent; He, Jiao; Kate, I. L. ten; Linnartz, H.

doi:10.3847/1538-4357/ab0d89

Cited by 27 publications

(40 citation statements)

References 51 publications

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“…The laser interference calibration method is limited to ices for which refractive indices are known (pure species). This might change as a result of a recently introduced new broad band technique, which holds the potential to also derive such parameters for mixed ices (Kofman et al 2019).…”

Section: Thickness Measurementsmentioning

confidence: 99%

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Bulak

Paardekooper

Fedoseev

et al. 2020

A&A

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Context. In cold regions of the interstellar medium with intense ultraviolet radiation fields, photodesorption has been suggested as a nonthermal desorption mechanism promoting the transition of molecules from the solid state to the gas phase. Laboratory experiments measuring photodesorption rates are crucial in attempting to explain high molecular gas phase abundances of species that are expected to form in the solid state, such as methane, methanol, and acetonitrile, and to aid astrochemical modeling. Due to the convoluted competition between photodesorption and photoconversion, it is far from trivial to derive accurate photodesorption rates. Aims. The aim of this study is to apply a new methodology to discriminate between the two processes. The method has been validated using the well-studied case of CO and extended to CH4, CH3OH, and CH3CN. Methods. Vacuum ultraviolet (VUV; photon energy of 7–10.2 eV) irradiated ices at 20 K are studied, first as a pure CH4, CH3OH, or CH3CN ice and subsequently with an Ar coating on top. The latter is transparent to the VUV photons (wavelength below 200 nm), but it quenches the photodesorption process. Comparing the laser desorption post ionization time-of-flight mass spectrometry of the ices with and without the Ar coating provides information on the different interactions of the VUV photons with the ice. Results. The newly developed experimental technique allowed for a derivation of photodesorption rates for ices at 20 K of: CO (3.1 ± 0.3)×10−3 mol. photon−1, CH4 (3.1 ± 0.5)×10−2 mol. photon−1, and upper limits for CH3OH (< 6 × 10−5 mol. photon−1) and CH3CN (< 7.4 × 10−4 mol. photon−1); in the latter case, no literature values have been reported yet. The newly introduced approach provides more insight into the photodesorption process, in particular, for commonly observed complex organic molecules (COMs). Photoconversion cross sections are presented in the 7–10.2 eV range. The possible role of photodesorption and photoconversion in the formation of interstellar COMs is discussed.

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Section: Thickness Measurementsmentioning

confidence: 99%

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Bulak

Paardekooper

Fedoseev

et al. 2020

A&A

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“…The growth rate of the ice is determined in advance using He-Ne laser (wavelength 632.8 nm) interference measurements (Baratta & Palumbo 1998;Bulak et al 2020). To calculate the deposition rate for H 2 O (background deposition) and CO 2 (front deposition), the refractive indices (1.2, and 1.21) and densities (0.94 g cm −3 , 0.98 g cm −3 ), respectively, are taken from the literature (Kofman et al 2019;Satorre et al 2008;Jenniskens et al 1998). In case of the deposition of H 2 O:CO 2 :O 2 , the mixture was premixed at the intended ratio and deposited through the front deposition capillary following a growth rate calibration for H 2 O and CO 2 .…”

Section: Methodsmentioning

confidence: 99%

Quantification of O₂ formation during UV photolysis of water ice: H₂O and H₂O:CO₂ ices

Bulak

Paardekooper

Fedoseev

et al. 2022

A&A

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Context. The Rosetta and Giotto missions investigated the composition of the cometary comae of 67P/Churyumov-Gerasimenko and 1P/Halley, respectively. In both cases, a surprisingly large amount of molecular oxygen (O 2 ) was detected and was well correlated with the observed abundances of H 2 O. Laboratory experiments simulating chemical processing for various astronomical environments already showed that formation of solid state O 2 is linked to water. However, a quantitative study of O 2 formation upon UV photolysis of pure H 2 O and H 2 O dominated interstellar ice analogues is still missing. Aims. The goal of this work is to investigate whether the UV irradiation of H 2 O-rich ice produced at the earliest stages of star formation is efficient enough to explain the observed abundance of cometary O 2 . Methods. The photochemistry of pure H 16 2 O (H 18 2 O) as well as mixed H 2 O:CO 2 (ratio of 100:11, 100:22, 100:44) and H 2 O:CO 2 :O 2 (100:22:2) ices was quantified during UV photolysis. Laser desorption post-ionisation time of flight mass spectrometry (LDPI TOF MS) was used to probe molecular abundances in the ice as a function of UV fluence. Results. Upon UV photolysis of pure amorphous H 2 O ice, deposited at 20 K, formation of O 2 and H 2 O 2 is observed at abundances of, respectively, (0.9 ± 0.2)% (O 2 /H 2 O) and (1.3 ± 0.3)% (H 2 O 2 /H 2 O). To the best of our knowledge, this is the first quantitative characterisation of the kinetics of this process. During the UV photolysis of mixed H 2 O:CO 2 ices, the formation of the relative amount of O 2 compared to H 2 O increases to a level of (1.6 ± 0.4)% (for H 2 O:CO 2 ratio of 100:22), while the (H 2 O 2 /H 2 O) yield remains similar to experiments with pure water. In an ice enriched with O 2 (2%), the O 2 level increases up to 7% with regard to H 2 O, at low UV fluence, which is higher than expected on the basis of the enrichment alone. The resulting O 2 /H 2 O values derived for the H 2 O and H 2 O:CO 2 ices may account for a (substantial) part of the high oxygen amounts found in the comae of 67P and 1P.

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“…However, the Lorentz-Lorenz relation may not be suitable for ASW. More recently, Kofman et al (2019) used a Xe arc "white" lamp and a UV-Vis spectrometer to measure the optical interference in the UV-Vis range and to derive the refractive index of vapor-deposited water ice within this wavelength range. The advantage of this method is that it allows measurement of the refractive index value over a large wavelength range in one-go, instead of performing measurements at each wavelength separately.…”

Section: Introductionmentioning

confidence: 99%

“…However, this method suffers from the same problem as described in previous studies, e.g., by Dohnálek et al (2003), i.e., that the density of the ice needs to be determined separately. Kofman et al (2019) used the density value obtained by Dohnálek et al (2003), assuming that the Lorentz-Lorenz relation is valid for ASW, to obtain the refractive index values in the UV-Vis range for water ice grown at different temperatures. To determine the refractive index value without relying on a separate calibration of density, Beltrán et al (2015) used a different approach in which two light sources at different incident angles are used to measure the optical interference.…”

Section: Introductionmentioning

confidence: 99%

“…However, the technique requires knowledge of the real and complex components of the refractive index of the substrate onto which the ice is grown; these data are not always available for a broad wavelength range and for cryogenic temperatures. In this study, we build upon existing work from Kofman et al (2019) and Beltrán et al (2015), using both a HeNe laser and Xe arc lamp at two different incidence angles to obtain the refractive index values in the UV-Vis range without relying on the separate calibration of ice thickness. This new approach comes with the advantages of both methods and does not rely on accurate optical parameters of the substrate.…”

Section: Introductionmentioning

confidence: 99%

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Refractive index and extinction coefficient of vapor-deposited water ice in the UV-Vis range

He,

Diamant,

Wang

et al. 2021

Preprint

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Laboratory results of the optical properties of vapor-deposited water ice, specifically the refractive index and extinction coefficient, are available mainly for a selective set of wavelengths and a limited number of deposition temperatures. Experimental limitations are the main reason for the lack of broadband data, which is unfortunate as these quantities are needed to interpret and predict astronomical and planetary observations. The goal of this work is to address these lacking data, using an experimental broadband method that is capable of rapidly providing reliable water ice data across the entire UV-visible range. This approach combines the simultaneous use of a monochromatic HeNe laser and a broadband Xe-arc lamp to record interference fringes of water ice during deposition at astronomically relevant ice temperatures. The ice thickness is typically more than 20 µm. Analyzing the period and intensity patterns combining both the monochromatic and broadband interference patterns allows the determination of the wavelength-dependent refractive index and extinction coefficient. We present accurate refractive index and extinction coefficient graphs for wavelengths between 250 and 750 nm and ices deposited between 30 and 160 K. From our data, we find a possible structural change in the ice in the 110-130 K region that has not been reported before. We also discuss that the data presented in this paper can be used to interpret astronomical observations of icy surfaces.

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The Refractive Index of Amorphous and Crystalline Water Ice in the UV–vis

Cited by 27 publications

References 51 publications

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Quantification of O₂ formation during UV photolysis of water ice: H₂O and H₂O:CO₂ ices

Refractive index and extinction coefficient of vapor-deposited water ice in the UV-Vis range

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The Refractive Index of Amorphous and Crystalline Water Ice in the UV–vis

Cited by 27 publications

References 51 publications

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Novel approach to distinguish between vacuum UV-induced ice photodesorption and photoconversion

Quantification of O2 formation during UV photolysis of water ice: H2O and H2O:CO2 ices

Refractive index and extinction coefficient of vapor-deposited water ice in the UV-Vis range

Contact Info

Product

Resources

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Quantification of O₂ formation during UV photolysis of water ice: H₂O and H₂O:CO₂ ices