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Pavithraa S, Ramachandran R, Mifsud DV, Meka JK, Lo JI, Chou SL, Cheng BM, Rajasekhar BN, Bhardwaj A, Mason NJ, Sivaraman B. VUV photoabsorption of thermally processed carbon disulfide and ammonia ice mixtures - Implications for icy objects in the solar system. Spectrochim Acta A Mol Biomol Spectrosc 2022; 283:121645. [PMID: 36037552 DOI: 10.1016/j.saa.2022.121645] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/24/2022] [Revised: 07/13/2022] [Accepted: 07/15/2022] [Indexed: 06/15/2023]
Abstract
Many icy bodies in the solar system have been found to contain a rich mixture of simple molecules on their surfaces. Similarly, comets are now known to be a reservoir of molecules ranging from water to amides. The processing of planetary/cometary ices leads to the synthesis of more complex molecules some of which may be the harbingers of life. Carbon disulphide (CS2) and ammonia (NH3) are known to be present on many icy satellites and comets. Reactions involving CS2 and NH3 may lead to the formation of larger molecules that are stable under space conditions. In this paper we present temperature dependent VUV spectra of pure CS2 in the ice phase, and of CS2 and NH3 ices deposited as (i) layered, and (ii) mixed ices at 10 K and warmed to higher temperatures until their sublimation. Pure CS2 ice is found to have a broad absorption in the VUV region, which is unique for a small molecule in the ice phase. In layered and mixed ices, the molecules tend to affect the phase change and sublimation temperature of each other and also leave behind a form of CS2-NH3 complex after thermal annealing. This study of CS2-NH3 ice systems in layered and mixed configurations would support the detection of these species/complexes in mixed molecular ices analogous to that on planetary and cometary surfaces.
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Affiliation(s)
- S Pavithraa
- Physical Research Laboratory, Ahmedabad, India
| | | | - D V Mifsud
- Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury CT2 7NH, UK; Institute for Nuclear Research (Atomki), Debrecen 4026, Hungary
| | - J K Meka
- Physical Research Laboratory, Ahmedabad, India
| | - J I Lo
- Department of Medical Research, Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Hualien, Taiwan
| | - S L Chou
- National Synchrotron Radiation Research Center, Taiwan
| | - Bing-Ming Cheng
- Department of Medical Research, Hualien Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, Hualien, Taiwan
| | | | | | - N J Mason
- Centre for Astrophysics and Planetary Science, School of Physical Sciences, University of Kent, Canterbury CT2 7NH, UK
| | - B Sivaraman
- Physical Research Laboratory, Ahmedabad, India.
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Waters MDJ, Wörner HJ. The ultrafast vibronic dynamics of ammonia's D̃ state. Phys Chem Chem Phys 2022; 24:23340-23349. [PMID: 36129030 DOI: 10.1039/d2cp03117e] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Using vacuum-ultraviolet time-resolved velocity map imaging of photoelectrons, we study ultrafast coupled electronic and nuclear dynamics in low-lying Rydberg states of ammonia. Vibrationally-resolved internal vibrational relaxation (IVR) is observed in a progression of the e' bending modes. This vibrational progression is only observed in the D̃ state, and is lost upon ultrafast internal conversion to the C̃ and B̃ electronic states. Due to the ultrashort time scale of the internal conversion (ca. 64 fs), and the vibronic resolution, the non-adiabatic coupling vectors are identified and verified with ab initio calculations. The time-scale of this IVR process is highly surprising and significant because IVR is usually treated as an incoherent process that proceeds statistically, according to a "Fermi's Golden Rule"-like model, where the process scales with the available degrees of freedom. Here, we show that it can be highly non-statistical, restricted to only a very small subset of vibrational motions.
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Affiliation(s)
- Max D J Waters
- Laboratory for Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland.
| | - Hans Jakob Wörner
- Laboratory for Physical Chemistry, ETH Zürich, Vladimir-Prelog-Weg 2, 8093, Zürich, Switzerland.
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González-Collado CM, Plésiat E, Decleva P, Palacios A, Martín F. Vibrationally resolved photoelectron angular distributions of ammonia. Phys Chem Chem Phys 2022; 24:7700-7712. [PMID: 35293411 DOI: 10.1039/d2cp00627h] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We present a theoretical study of vibrationally resolved photoelectron angular distributions for ammonia in both laboratory and molecular frames, in the photon energy range up to 70 eV, where only valence and inner-valence ionization is possible. We focus on the band resulting from ionization of the 3a1 HOMO orbital leading to NH3+ in the electronic ground state, , for which the dominant vibrational progression corresponds to the activation of the umbrella inversion mode. We show that, at room temperature, the photoelectron angular distributions for randomly oriented molecules or molecules whose principal C3 symmetry axis is aligned along the light polarization direction are perfectly symmetric with respect to the plane that contains the intermediate D3h conformation connecting the pyramidal structures associated with the double-well potential of the umbrella inversion mode. These distributions exhibit symmetric, nearly perfect two-lobe shapes in the whole range of investigated photon energies. In contrast, for molecules where the initial vibrational state is localized in one of the two wells, a situation that can experimentally be achieved by introducing an external electric field, the molecular-frame photoelectron angular distributions (MFPADs) are in general asymmetric, but the degree of asymmetry of the two lobes dramatically changes and oscillates with photoelectron energy. We also show that, at ultracold temperatures, where all aligned molecules initially lie in the delocalized ground vibrational state, the photoelectron angular distributions are perfectly symmetric, but the two-lobe shape is only observed when the final vibrational state of the resulting NH3+ cation has even parity. When the latter vibrational state has odd parity, the angular distributions are much more involved and, at photoelectron energies of ∼10 eV, they directly reflect the bi-pyramidal geometry of the molecule in its ground vibrational state. These results suggest that, in order to obtain structural information from MFPADs in ammonia and likely in other molecules containing a similar double-well potential, one could preferably work at ultracold temperatures, which is not the case for most molecules.
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Affiliation(s)
| | - Etienne Plésiat
- Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain
| | - Piero Decleva
- Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste and CNR-IOM, 34127 Trieste, Italy
| | - Alicia Palacios
- Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain. .,Institute of Advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain
| | - Fernando Martín
- Departamento de Química, Módulo 13, Universidad Autónoma de Madrid, 28049 Madrid, Spain. .,Instituto Madrileño de Estudios Avanzados en Nanociencia (IMDEA-Nanociencia), Cantoblanco, 28049 Madrid, Spain.,Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, 28049 Madrid, Spain
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Abstract
We trace a polymorphic phase change in solid ammonia films through the emergence of a Frenkel exciton at 194.4 nm, for deposition temperatures of 48 K, 50 K and 52 K. Observations on a timescale of hours give unparalleled access to the individual processes of nucleation and the phase change itself. The excitonic transition is forbidden in the low temperature phase, but greater flexing of the solid state structure in the higher temperature phase makes the transition allowed, as the nano-crystals approach ∼30 unit cells through nucleation. We find activation energies of 21.7 ± 0.6 kJ mol-1 for nucleation and 22.8 ± 0.6 kJ mol-1 for the phase change, corresponding to the breaking of two to three hydrogen bonds.
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Affiliation(s)
- Andrew Cassidy
- Center for Interstellar Catalysis and Department of Physics and Astronomy, Aarhus University, Denmark.
| | - Rachel L James
- Department of Earth and Environmental Sciences, University of Manchester, UK
| | - Anita Dawes
- School of Physical Sciences, The Open University, UK.
| | - David Field
- Department of Physics and Astronomy, Aarhus University, Denmark
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Weng W, Li S, Aldén M, Li Z. Ultraviolet Absorption Cross-Sections of Ammonia at Elevated Temperatures for Nonintrusive Quantitative Detection in Combustion Environments. Appl Spectrosc 2021; 75:1168-1177. [PMID: 33464157 PMCID: PMC8446901 DOI: 10.1177/0003702821990445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/11/2020] [Accepted: 01/05/2021] [Indexed: 06/12/2023]
Abstract
Ammonia (NH3) is regarded as an important nitrogen oxides (NOx) precursor and also as an effective reductant for NOx removal in energy utilization through combustion, and it has recently become an attractive non-carbon alternative fuel. To have a better understanding of thermochemical properties of NH3, accurate in situ detection of NH3 in high temperature environments is desirable. Ultraviolet (UV) absorption spectroscopy is a feasible technique. To achieve quantitative measurements, spectrally resolved UV absorption cross-sections of NH3 in hot gas environments at different temperatures from 295 K to 590 K were experimentally measured for the first time. Based on the experimental results, vibrational constants of NH3 were determined and used for the calculation of the absorption cross-section of NH3 at high temperatures above 590 K using the PGOPHER software. The investigated UV spectra covered the range of wavelengths from 190 nm to 230 nm, where spectral structures of the A∼ 1A″2X∼ 1A'1 transition of NH3 in the umbrella bending mode, v2, were recognized. The absorption cross-section was found to decrease at higher temperatures. For example, the absorption cross-section peak of the (6, 0) vibrational band of NH3 decreases from ∼2 × 10-17 to ∼0.5 × 10-17 cm2/molecule with the increase of temperature from 295 K to 1570 K. Using the obtained absorption cross-section, in situ nonintrusive quantification of NH3 in different hot gas environments was achieved with a detection limit varying from below 10 parts per million (ppm) to around 200 ppm as temperature increased from 295 K to 1570 K. The quantitative measurement was applied to an experimental investigation of NH3 combustion process. The concentrations of NH3 and nitric oxide (NO) in the post flame zone of NH3-methane (CH4)-air premixed flames at different equivalence ratios were measured.
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Affiliation(s)
- Wubin Weng
- Wubin Weng, Lunds Universitet, PO Box 118,
Lund 221 00, Sweden.
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Abstract
Absorption spectra of vacuum-deposited films of ammonia have been obtained in the range 115 nm to 310 nm for a set of 15 deposition temperatures, Td, between 20 K and 80 K. Results focus upon the region 115 nm to 130 nm in overlapping D, E, F and G←X Rydberg transitions involving Wannier-Mott excitons. We identify two phases of ammonia, showing the solid to be polymorphic. Peak absorption wavelengths in the region of interest are found to shift to the red by 299 cm-1, for Td between 20 K to 50 K, and 1380 cm-1 for Td between 55 K to 80 K. Shifts provide evidence for the presence of spontaneously generated electric fields in these films, of values in excess of 108 V m-1 for Td of 20 K to 50 K to a few times 107 V m-1 for 55 K to 80 K. Results enable us to place a lower limit of 1.58 nm on the size of crystallites in the low temperature regime. This dimension represents 16 unit cells or 64 species, giving a more quantitative description than the nebulous term amorphous, as applied to solid ammonia. We also determine that crystallites formed in the high temperature regime contain, within ±20 %, 1688, 756 and 236 molecules of ammonia, respectively at Td of 65 K, 60 K and 55 K.
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Affiliation(s)
- Andrew Cassidy
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus, Denmark
| | - Rachel L James
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
| | - Anita Dawes
- School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
| | - David Field
- Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000, Aarhus, Denmark
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Bielecki Z, Stacewicz T, Smulko J, Wojtas J. Ammonia Gas Sensors: Comparison of Solid-State and Optical Methods. Applied Sciences 2020; 10:5111. [DOI: 10.3390/app10155111] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
High precision and fast measurement of gas concentrations is important for both understanding and monitoring various phenomena, from industrial and environmental to medical and scientific applications. This article deals with the recent progress in ammonia detection using in-situ solid-state and optical methods. Due to the continuous progress in material engineering and optoelectronic technologies, these methods are among the most perceptive because of their advantages in a specific application. We present the basics of each technique, their performance limits, and the possibility of further development. The practical implementations of representative examples are described in detail. Finally, we present a performance comparison of selected practical application, accumulating data reported over the preceding decade, and conclude from this comparison.
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