Browsing by Author "Mason, N. J."

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Identification of a unique VUV photoabsorption band of carbonic acid for its identification in radiation and thermally processed water-carbon dioxide ices
(2019-05-15)
Pavithraa, S.
;
Lo, J-, I
;
Cheng, B-M
;
Sekhar, B. N. Raja
;
Mason, N. J.
Carbonic acid was synthesized within an ice containingwater and carbon dioxide by irradiation of similar to 9 eV photons. Vacuum UltraViolet (VUV)/UltraViolet (UV) photoabsorption spectra of the irradiated ice revealed absorption features from carbon dioxide, ozone, water, carbon monoxide and oxygen in addition to a band peaking at similar to 200 nm which is identified to be characteristic of carbonic acid. After thermal processing of the irradiated ice leading to desorption of the lower volatile ices, a pure carbonic acid spectrum is identified starting from 170 K until sublimation above 230 K. Therefore the similar to 200 nm band in the VUV region corresponding to carbonic acid is proposed to be a unique identifier in mixed ices, rich in water and carbon dioxide typically encountered on planetary and satellite surfaces. (C) 2019 Elsevier B.V. All rights reserved.
Infrared attenuation due to phase change from amorphous to crystalline observed in astrochemical propargyl ether ices
(2020-01-05)
Rahul, K. K.
;
Meka, J. K.
;
Pavithraa, S.
;
Gorai, P.
;
Das, A.
Astrochemical ices are known to undergo morphological changes, from amorphous to crystalline, upon warming the ice from lower (10 K) to higher temperatures. Phase changes are mostly identified by the observation of significant changes in the InfraRed (IR) spectrum, where the IR bands that are broad in the amorphous phase are narrower and split when the ice turns crystalline. To-date all the molecules that are studied under astrochemical conditions are observed to follow such a behaviour without significant attenuation in the IR wavelength. However, in this paper we report a new observation when propargyl ether (C3H3OC3H3) is warmed from the amorphous phase, at 10 K, through the phase transition temperature of 170 K, the crystalline ice being found to strongly attenuate IR photons at the mid-IR wavelengths. (c) 2019 Elsevier B.V. All rights reserved.
Qualitative observation of reversible phase change in astrochemical ethanethiol ices using infrared spectroscopy
(2017-05-05)
Pavithraa, S.
;
Methikkalam, R. R. J.
;
Gorai, P.
;
Lo, J-I
;
Das, A.
Here we report the first evidence for a reversible phase change in an ethanethiol ice prepared under astrochemical conditions. InfraRed (IR) spectroscopy was used to monitor the morphology of the ice using the S H stretching vibration, a characteristic vibration of thiol molecules. The deposited sample was able to switch between amorphous and crystalline phases repeatedly under temperature cycles between 10 K and 130 K with subsequent loss of molecules in every phase change. Such an effect is dependent upon the original thickness of the ice. Further work on quantitative analysis is to be carried out in due course whereas here we are reporting the first results obtained. (C) 2017 Elsevier B.V. All rights reserved.
SH stretching vibration of propanethiol ice-a signature for its identification in the interstellar icy mantles
(2017-07-01)
Pavithraa, S.
;
Sahu, D.
;
Seth, G.
;
Lo, J. -I.
;
Sekhar, B. N. Raja
Among the most commonly existing thiol molecules, methanethiol and ethanethiol were discovered in the interstellar medium and identification of the next larger thiol molecule, propanethiol, is long awaited. By simulating icy astrochemical conditions and probing propanethiol ices under infrared spectroscopy we propose the use of SH stretching vibrations observed in the propanethiol molecular ice as a probe towards its identification in the interstellar medium. Though there are conformational changes within the ice (as observed in both VUV and IR spectra), the SH stretching vibration of propanethiol is observed to be unique among the set of thiol molecules, methanethiol and ethanethiol, which enables the detection of propanethiol ice in interstellar dust mantles using the James Webb Space Telescope.
Vacuum ultraviolet photoabsorption of prime ice analogues of Pluto and Charon
(2018-02-05)
Pavithraa, S.
;
Lo, J-I
;
Rahul, K.
;
Sekhar, B. N. Raja
;
Cheng, B-M.
Here we present the first Vacuum UltraViolet (VUV) photoabsorption spectra of ice analogues of Pluto and Charon ice mixtures. For Pluto the ice analogue is an icy mixture containing nitrogen (N-2), carbon monoxide (CO), methane (CH4) and water (H2O) prepared with a 100:1:1:3 ratio, respectively. Photoabsorption of icy mixtures with and without H2O were recorded and no significant changes in the spectra due to presence of H2O were observed. For Charon a VUV photoabsorption spectra of an ice analogue containing ammonia (NH3) and H2O prepared with a 1:1 ratio was recorded, a spectrum of ammonium hydroxide (NH4OH) was also recorded. These spectra may help to interpret the P-Alice data from New Horizons. (C) 2017 Elsevier B.V. All rights reserved.