Browsing by Author "Amit Pathak"

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A comprehensive rotational study of astronomical iso-pentane within 84 to 111 GHz
(Elsevier B.V., 2023) Anshika Pandey; Satyam Srivastav; Akant Vats; Amit Pathak; K.A.P. Singh
The rotational line survey by ALMA (Atacama Large Millimeter/submillimeter Array) recently revealed the presence of i-C3H7CN (i-PrCN) and n-C3H7CN (n-PrCN) in 3-mm atmospheric window between 84 to 111 GHz towards the hot core region Sagittarius B2(N) (Sgr B2(N)). This was the first interstellar detection of a linear straight chain molecule. In this light, we report the rotational spectra of C5H12 isomeric group in the same frequency range. We performed quantum chemical calculations for spectroscopic parameters. The pure rotational spectrum of the species has been simulated using the PGOPHER program. The rotational spectrum of this molecule makes it a good candidate for future astronomical detections since the radio lines can be calculated to very high accuracy in mm/sub-mm wave region. © 2022 Elsevier B.V.
A study of highly sensitive D-shaped optical fiber surface plasmon resonance based refractive index sensor using grating structures of Ag-TiO2 and Ag-SnO2
(Elsevier GmbH, 2022) Sarvesh K. Dubey; Anil Kumar; Awadhesh Kumar; Amit Pathak; S.K. Srivastava
In this study, we propose a design and simulation of a highly sensitive surface plasmon resonance (SPR) based single-mode D-shaped optical fiber refractive index sensor in the near-infrared (NIR) region. It consists grating structure of silver coated with titanium dioxide (TiO2) and Tin dioxide (SnO2) layer on the core-cladding interface. With the help of the finite element method (FEM), the proposed optical fiber sensors are optimized with various geometrical parameters. Proposed optimized structures are investigated and various performance parameters are calculated. It is found that performance parameters enhance with TiO2/SnO2 coated on Ag grating structure at a particular thickness of TiO2/SnO2. Due to this more generations of surface plasmons take place on metal-metal oxide structures. We find the maximum sensitivity of 15.31 μm / RIU and 9.81 μm / RIU for Ag-TiO2 and Ag-SnO2 grating structure respectively which shows a better result in comparison to the other reported work. So proposed structure may have great potential to enhance the sensing ability of optical fiber-based sensors as compared to the other conventional SPR based optical fiber sensors. © 2021 Elsevier GmbH
A Study of Sensitivity Improved Probe Using Hyperbolic Metamaterial for Optical Fiber SPR (OFSPR)-based Refractive Index Sensor
(Springer, 2022) Sarvesh Kumar Dubey; Anil Kumar; Amritanshu Pandey; Amit Pathak; S.K. Srivastava
In this work, we theoretically study the plasmonic behavior of Ag and Au with a hyperbolic metamaterial (HMM) and propose a numerical simulation of a D-shaped surface plasmon resonance (SPR)-based refractive index sensor in the near-infrared (NIR) region using the finite element method (FEM). The design of the sensing probe consists of a grating structure of metal (Ag/Au) coated with an alpha-phase molybdenum trioxide (α-MoO3) HMM layer. The sensing layer of α-MoO3 over Ag/Au is responsible for the enhanced sensitivity of the optical fiber SPR sensor. This is attributed to the better SPR generation with a metal-dielectric layer. Numerical results show that the proposed sensor is able to detect a refractive index over a large dynamic range of 1.33 to 1.4. With the help of the optimized structure, we achieve maximum sensitivity of 8.31 μm /RIU and 9.89 μm /RIU for the Ag-α-MoO3- and Au-α-MoO3-based grating structure, respectively. These results show excellent response in comparison with other reported works. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.
Astrochemical model to study the abundances of branched carbon-chain molecules in a hot molecular core with realistic binding energies
(Oxford University Press, 2022) Satyam Srivastav; Milan Sil; Prasanta Gorai; Amit Pathak; Bhalamurugan Sivaraman; Ankan Das
Straight-chain (normal-propyl cyanide, $\rm {n-C_3H_7CN}$) and branched-chain (iso-propyl cyanide, $\rm {i-C_3H_7CN}$) alkyl cyanides are recently identified in the massive star-forming regions (Sgr B2(N) and Orion). These branched-chain molecules indicate that the key amino acids (side-chain structures) may also be present in a similar region. The process by which this branching could propagate towards the higher order (butyl cyanide, $\rm {C_4H_9CN}$) is an active field of research. Since the grain catalysis process could have formed a major portion of these species, considering a realistic set of binding energies are indeed essential. We employ quantum chemical calculations to estimate the binding energy of these species considering water as a substrate because water is the principal constituent of this interstellar ice. We find significantly lower binding energy values for these species than were previously used. It is noticed that the use of realistic binding energy values can significantly change the abundance of these species. The branching is more favourable for the higher order alkyl cyanides with the new binding energies. With the inclusion of our new binding energy values and one essential destruction reaction ($\rm {i-C_3H_7CN+H \rightarrow CH_3C(CH_3)CN + H_2}$, having an activation barrier of 947 K), abundances of $\rm {t-C_4H_9CN}$ dramatically increased. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.
C-H Stretch Vibrational Modes: Tracers of Interstellar PAH Geometries?
(American Chemical Society, 2023) Akant Vats; Amit Pathak; Takashi Onaka; Itsuki Sakon; Izumi Endo
Polycyclic aromatic hydrocarbon (PAH) molecules have long been adjudged as carriers of the frequently detected interstellar emission features in the 3-20 μm region. In the present work, PAHs with straight edges having solo-duo (PAHD) and solo-duo-trio (PAHT) C-H modes along with PAHs with irregular edges (PAHI) have been studied theoretically to understand the effect of molecular geometry on the interstellar C-H stretch vibrations at 3.3 μm. The C-H out-of-plane bending vibrations at 11.2 and 12.7 μm are also included for completeness. Using the NASA Ames PAH IR Spectroscopic Database, the mid-infrared spectra have been studied for 125 PAH molecules of varying molecular geometries, sizes, charge states, and symmetries. Results show that the individual solo, duo, and trio C-H stretches follow an order in the peak wavelength (λ3.3 (solo) > λ3.3 (duo) > λ3.3 (trio)) and intensity (I3.3 (solo) < I3.3 (duo) < I3.3 (trio)). If only PAHD’s are considered, the contribution of each charge state is required to account for the observed peak wavelength of the 3.3 μm band, or if only neutrals are contributors, PAHD and PAHT neutrals can explain the 3.3 μm band variations. The observed emission at 11.2 and 12.7 μm is found to match effectively with PAHD with increasing size, and the 11.2 μm band is present at longer wavelengths for PAHT contributing to the red wing. When the solo to duo hydrogen ratio is nearly equal to or greater than 1.0, PAHD neutrals yield better 3.3 μm peak positions. The ratio has a lower limit of 0.8 for the 11.2 μm band and converges at 1.5, indicating a size range of PAHD neutrals with 80 to larger numbers of carbon atoms. The present work examines the presence of solo, duo, and trio modes in the C-H stretching band, which must be taken into consideration when interpreting accurate data from James Webb Space Telescope (JWST) to further explain the observed variations in the interstellar 3.3 μm. © 2023 American Chemical Society.
CeO2 Nanocubes as an Electrochemical Sensing Platform for Simultaneous Detection of Dopamine and Acetaminophen
(Institute of Physics, 2025) Ashish Kumar; Mohd Ali; Amit Pathak; Debanjan Guin; Chandra Shekhar Pati Tripathi
The overlapping redox potentials of analytes and the lack of selectivity present significant challenges for unmodified electrodes in electrochemical sensing. In this work, we have fabricated an electrochemical sensor based on cerium oxide nanocubes (CeO2-NCs) coated glassy carbon electrode (CeO2-NCs@GCE) for individual and simultaneous detection of dopamine (DA) and acetaminophen (APAP) with high sensitivity and selectivity. The CeO2-NCs were synthesized using a one-step hydrothermal method and characterized by Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and Raman spectroscopy. Cyclic voltammetry and electrochemical impedance spectroscopy were employed for electrochemical characterizations. With improved electrocatalytic redox activity due to enhanced active surface area and reduced interfacial charge transfer resistance, CeO2-NCs@GCE shows superior detection efficiency. The detection of DA and APAP was evaluated using differential pulse voltammetry. Low detection limit values of 0.696 μM for DA and 0.341 μM for APAP with a wide linear range of 10-400 μM applicability were achieved. The CeO2-NCs@GCE sensor was also used to detect DA in DA injection and APAP in paracetamol tablet samples. The developed sensor demonstrated satisfactory recovery results ranging from 96.5 to 102.8% in pharmaceutical samples, confirming the applicability of the proposed method for simultaneous detection of DA and APAP in real samples. © 2025 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
CeO2 nanosheets with prominent peroxidase-mimicking activity for the colorimetric sensing of H2O2, glucose, and ascorbic acid
(Elsevier B.V., 2025) Ashish Kumar; Renuka Singh; Amit Pathak; Debanjan Guin; Chandra Shekhar Pati Tripathi
The peroxidase-mimicking activity of nanozymes has been extensively utilized in the colorimetric turn-on detection of hydrogen peroxide (H2O2) and compounds that produce H2O2 as an intermediate, facilitating the identification of small biological molecules through oxidative chromogenic reactions. In this report, the peroxidase-mimic activity of Cerium Oxide nanosheets (CeO2 NSs) as a nanozyme has been thoroughly investigated. CeO2 NSs were synthesized using a simple, cost-effective one-step sugar-blowing method and characterized by various analytical techniques. CeO2 NSs catalyze to oxidize the peroxidase substrate 3,3′,5,5′-tetramethylbenzidine (TMB) into Ox-TMB in the presence of H2O2, producing a blue color (turn-on). The CeO2 NSs-based colorimetric assay was successfully used to detect H2O2 and glucose. The linear detection ranges for turn-on sensing were found to be 11 µM–455 µM for H2O2, and 5.43 µM–86.95 µM and 86.95 µM–347.82 µM for glucose. The limits of detection (LOD) were calculated as 1.613 μM for H2O2 and 1.068 μM for glucose. Blue-colored Ox-TMB turns colorless with the addition of ascorbic acid; using this colorimetric turn-off mechanism, CeO2 NSs were also able to detect ascorbic acid within the range of 2.2–21.73 μM, with a LOD of 0.058 μM. Satisfactory recovery rates were observed in fruit samples, showing the effectiveness of the sensor in practical applications. © 2025 The Authors
Chemical Complexity of Phosphorous-bearing Species in Various Regions of the Interstellar Medium
(American Astronomical Society, 2021) Milan Sil; Satyam Srivastav; Bratati Bhat; Suman Kumar Mondal; Prasanta Gorai; Rana Ghosh; Takashi Shimonishi; Sandip K. Chakrabarti; Bhalamurugan Sivaraman; Amit Pathak; Naoki Nakatani; Kenji Furuya; Ankan Das
Phosphorus-related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this paper, we carry out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos. We notice a curious correlation between the abundances of PO and PN and atomic nitrogen. Since N atoms are more abundant in diffuse clouds and PDRs than in the hot core/corino region, PO/PN reflects <1 in diffuse clouds, ≪1 in PDRs, and >1 in the late warm-up evolutionary stage of the hot core/corino regions. During the end of the post-warm-up stage, we obtain PO/PN > 1 for hot core and <1 for its low-mass analog. We employ a radiative transfer model to investigate the transitions of some of the P-bearing species in diffuse cloud and hot core regions and estimate the line profiles. Our study estimates the required integration time to observe these transitions with ground-based and space-based telescopes. We also carry out quantum chemical computation of the infrared features of PH3, along with various impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes around ∼1000-1100 cm-1. We also find that the presence of CO2 can strongly influence the intensity of the stretching modes around ∼2400 cm-1 of PH3. © 2021. The American Astronomical Society. All rights reserved..
DFT study of five-membered ring PAHs
(Elsevier Ltd, 2020) Gauri Devi; Mridusmita Buragohain; Amit Pathak
This work reports a ‘Density Functional Theory’ (DFT) calculation of PAH molecules with a five-member ring to determine the expected region of infrared features. It is highly possible that fullerene molecule might be originated from five-membered ring PAH molecules in the ISM. Effect of ionization and protonation on five-membered ring PAH molecule is also discussed. A detail vibrational analysis of five-membered ring PAH molecule has been reported to further compare with observations and to identify any observational counterpart. © 2018 Elsevier Ltd
DFT study of Interstellar PANH: Vibrational spectra of anionic and cationic variants
(Elsevier Ltd, 2022) Gauri Devi; Amit Pathak; Akant Vats
Polycyclic aromatic Hydrocarbons are present in the universe in varied forms and are extensively studied over the years to account for the complex natured Aromatic Infrared Bands (AIBs). As an abundant element in the interstellar medium, nitrogen may substitute carbon atoms in the aromatic rings of PAHs to form Polycyclic Aromatic Nitrogen Heterocyclic (PANH) molecules. These PANH molecules can have new emission features and may contribute to some of the AIBs. Extreme conditions of the ISM may support PAH and/or PANH molecules in the formation of their cationic or anionic forms to further explain the AIBs. The present work reports DFT study of PANH molecules and their ionized variants and discusses their IR spectroscopic features in the 6–10 μm region. © 2022
DFT Study on Interstellar PAH Molecules with Aliphatic Side Groups
(Institute of Physics Publishing, 2020) Mridusmita Buragohain; Amit Pathak; Itsuki Sakon; Takashi Onaka
Polycyclic aromatic hydrocarbon (PAH) molecules have been long adjudged to contribute to the frequently detected distinct emission features at 3.3, 6.2, 7.7, 8.6, 11.2, and 12.7 μm with weaker and blended features distributed in the 3-20 μm region. The comparatively weaker 3.4 μm emission feature has been attributed to have an aliphatic origin as carrier. PAH with an aliphatic functional group attached to it is one of the proposed potential candidate carriers for the 3.4 μm emission band, however, the assignment of carrier is still enigmatic. In this work, we employ density functional theory calculation on a symmetric and compact PAH molecule; coronene (C24H12) with aliphatic side group to investigate any spectral similarities with observed features at 3-4 μm. The side groups considered in this study are-H (hydrogenated),-CH3 (methyl),-CH2-CH3 (ethyl), and-CH=CH2 (vinyl) functional groups. Considering the possible presence of deuterium (D) in PAHs, we also include D in the aliphatic side group to study the spectral behavior. We present a detailed analysis of the IR spectra of these molecules and discuss possible astrophysical implications. © 2020. The American Astronomical Society. All rights reserved.
Direct Observations of Different Sunspot Waves Influenced by Umbral Flashes
(Institute of Physics Publishing, 2017) Aishawnnya Sharma; G.R. Gupta; Durgesh Tripathi; V. Kashyap; Amit Pathak
We report the simultaneous presence of chromospheric umbral flashes and associated umbral waves, and propagating coronal disturbances, in a sunspot and related active region. We have analyzed time-distance maps obtained using the observations from the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. These maps show the simultaneous occurrence of different sunspot oscillations and waves such as umbral flashes, umbral waves, and coronal waves. Analysis of the original light curves, i.e., without implementing any Fourier filtering on them, shows that the amplitudes of different sunspot waves observed at different atmospheric layers change in synchronization with the light curves obtained from the umbral flash region, thus demonstrating that these oscillations are modulated by umbral flashes. This study provides the first observational evidence of the influence of sunspot oscillations within the umbra on other sunspot waves extending up to the corona. The properties of these waves and oscillations can be utilized to study the inherent magnetic coupling among different layers of the solar atmosphere above sunspots. © 2017. The American Astronomical Society. All rights reserved.
Enhanced dielectric and electrical properties of polystyrene-2% divinyl benzene (PDB) embedded in SrTiO3-Poly (vinylidene fluoride) three phase composite films
(Elsevier GmbH, 2022) N.P. Yadav; Bibhuti B. Sahu; Tarun Yadav; Rajneesh Kumar; Amit Pathak; G.N. Pandey; Srikanta Moharana
A facile solution casting technique has been employed to fabricate ceramic SrTiO3; STO particle and polystyrene-2% divinyl benzene (PDB) filled three phase composite films using poly(vinylidene fluoride) (PVDF) matrix. The frequency dependence of dielectric and electrical properties of the three phase PVDF-STO-PDB composite films of various weight percentage of PDB (fPDB) were analyzed. With the small change in the AC conductivity and dielectric loss the dielectric constant of the PVDF-STO-PDB composite systems is improved noticeably. The experimental results suggested that, the introduction of 10 wt% of PDB particles in the PVDF-STO composites enhanced the dielectric constant (≈76) and suppressed dielectric loss value (< 0.5) at 100 Hz. This may be attributed to the addition of PDB particles improved the establishment of polarization. The morphological analysis depicts that the PDB particles are uniformly dispersed and well compatibility between filler particles and polymer matrix which may be ascribed to the minimization of dielectric loss of the resultant composites. Further, the strong interaction between PDB particles and PVDF matrix at the interface is the crucial factor in the improvement of the dielectric and electrical properties. The percolation theory was used to elucidate the dielectric and electrical performance of PVDF-STO-PDB composites. It is noticed that the three phase PVDF-STO-PDB composite films exhibited an insulator-conductor transition with percolation threshold of fPDB = 5 wt%. The three phase composites with high dielectric constant (≈76) at percolation threshold might be helpful to understand the influence of PDB particles on the interfaces between the ceramics and polymer matrix. This work will provide an easy and effective solution to fabricate high performance three phase composites to the development of high energy storage applications. © 2022 Elsevier GmbH
Enhanced dielectric and electrical properties of tri-phase percolative PVDF–BiFeO3–Carbon Black (CB) composite film
(Springer, 2021) Srikanta Moharana; Tarun Yadav; Parvez Ahmad Alvi; Amit Pathak; R.N. Mahaling
A tri-phase polymer composite film with a multiferroic phase (BiFeO3) and conductive carbon black (CB) deposited on the BiFeO3 (BF) and poly(vinylidene fluoride) (PVDF) matrix were prepared by using a solution casting technique. The dielectric and electrical performance of BF–PVDF composites with various weight percentages of CB content was studied. It has been observed that the incorporation of high loading of CB to the BF–PVDF composite system led to a significant improvement in the dielectric constant with suppressed dielectric loss (< 0.5). The high dielectric constant of 69 at 100 Hz, which is 11 times greater than that of neat PVDF film with a lower dielectric loss of 0.41, is obtained for PVDF–BF–CB composites as CB content (8 wt%) approached the percolation threshold. Furthermore, the improvement of dielectric and electrical performance of the PVDF–BF–CB composites may be due to the synergistic effect of the multiferroic phase BF and conductive phase CB as a result of homogeneous dispersion within the polymer matrix. These high dielectric constant and suppressed dielectric loss PVDF–BF–CB composites might be suitable for potential applications in the field of future thin-film capacitors. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.
Enhanced Visible Light Photocatalytic Performance of CeO2@Acidified g-C3N4 Nanoheterostructures for RhB Degradation
(American Chemical Society, 2025) Ashish Kumar; Vaibhav Arya; Amit Pathak; Suverna Trivedi; Debanjan Guin; Chandra Shekhar Pati Tripathi
Photocatalysis with visible light is emerging as an effective solution for tackling environmental concerns, specifically focusing on the removal of dye pollution from wastewater. In this work, we have developed a scalable and efficient route for the synthesis of a (CeO2@CN) nanocomposite by in situ co-pyrolysis of the cerium adipate complex and melamine, followed by acidification and exfoliation of the nanocomposite (CeO2@A-gCN) for the degradation of rhodamine (RhB) dye in visible light. The synthesized photocatalysts were characterized by sophisticated techniques: X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, UV-vis diffuse reflectance spectroscopy, zeta potential, Brunauer-Emmett-Teller surface area measurements, and electrochemical impedance spectroscopy. The microstructure analysis confirmed the formation of an effective n-n type heterojunction with intimate close contact. The sample 3%CeO2@A-gCN shows complete degradation compared to pristine CN (63%) and 3%CeO2@CN (70%) with respective rate constant values of 0.011, 0.005, and 0.006 min-1. The enhanced photocatalytic efficiency was due to synergistic interaction between the energy levels of CeO2 and A-gCN, leading to highly improved photogenerated charge carrier separation, enhancement in specific surface area, reduced interfacial charge transfer resistance, and improved charge carrier transport. The charge separation and degradation mechanism was investigated in detail using photoluminescence spectroscopy, quenching and quantification experiments, and transient current response under light irradiation. 3%CeO2@A-gCN demonstrated consistent stability, highlighting its suitability for practical wastewater treatment applications. © 2025 American Chemical Society.
Evidence for coronal temperature variation in seyfert 2 ESO 103-035 Using NuSTAR observations
(IOP Publishing Ltd, 2021) Samuzal Barua; V. Jithesh; Ranjeev Misra; Gulab C. Dewangan; Rathin Sarma; Amit Pathak; Biman J. Medhi
We report flux-resolved spectroscopic analysis of the active galactic nucleus (AGN) ESO 103-035 using NuSTAR observations. Following an earlier work, we fit the spectra using a thermal Comptonization model with a relativistic reflection component to obtain estimates of the coronal temperature for two flux levels. The coronal temperature was found to increase from - 24.0+3.4 6.8 to - 55.3+ keV 7.2 54.6 (errors at the 1s confidence level) as the flux increased from 9.8 to 11.9 × 10-11 erg cm-2 s-1 in the 3-78 keV band. A marginal variation in the high energy photon index allows for both a nonvarying optical depth and for the optical depth to have varied by a factor of ~2. This is in contrast to a previous work on NuSTAR flux-resolved spectroscopy of the AGN, Ark 564, where the temperature was found to decrease with flux along with a 10% variation in the optical depth. The results may be understood in a framework where AGN variability is either dominated by coronal heating variation leading to a correlated increase of temperature with flux or the opposite effect being seen when the variability is dominated by changes in the seed photon flux. © 2021. The American Astronomical Society.
Formation routes, structures, and spectroscopic parameters of butyl isocyanides: The case of t-C4H9NC isomer in TMC-1
(Oxford University Press, 2025) Satyam Srivastav; Vincenzo Barone; Akant Vats; Anshika Pandey; Luigi Crisci; Shivani Mishra; Amit Pathak; Liton Majumdar
Cyanides and isocyanides are key prebiotic molecules in the interstellar medium, although the latter have been rarely detected. The observed variations in the isocyanide-to-cyanide ratio among different sources indicate incomplete understanding of their formation chemistry. We report a comprehensive computational study of the conformational landscape of butyl isocyanides (n-, i-, s-, and t-CHNC), including structural and spectroscopic characterization of the low-energy conformers. Equilibrium geometries and rotational constants were obtained using the Pisa Composite Schemes combined with second-order vibrational perturbation theory, yielding mean deviations from experimental data of 0.1 per cent, equivalent to 1 mÅ in bond lengths and in bond angles. Simulated rotational spectra in the 20-200 GHz range show that the most intense transitions of all isomers occur mainly between 75 and 160 GHz at 100-300 K, shifting to 50-110 GHz at 10 K. Formation and destruction pathways of t-CHNC and its precursors were analysed under cold interstellar conditions, and global rate coefficients were derived for chemical modelling. The predicted abundance of t-CHNC is very low (1.45 10), consistent with its current non-detection in astronomical surveys. © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society.
Infrared spectra of protonated and deuteronated C 60 in interstellar environments
(Springer, 2023) Akant Vats; Amit Pathak
With the credible detection of C60, C70 and C70+ in the interstellar medium (ISM), new prospects have opened up for the search of other fullerenes and their derivatives. Since fullerenes show high proton affinities, their protonated forms should predominate in the ISM, which can easily go through deuterium enrichment. Here, we present the infrared (IR) spectra and standard enthalpy of formation of C60H+, C60D+, C60H18+ and C60D18+ using Density Functional Theory (DFT) in singly ionized forms. The obtained computed IR spectra are compared with the observations. The results show that the four mid-infrared bands of neutral C60 are still visible in C60H+ and C60D+, but their strength diminishes in C60H18+ and C60D18+. As a conclusion, it is possible that the IR bands ascribed to C60 are a mixture of pure and slightly protonated and deuteronated fullerenes. In this way, the observed scattering of the C60 band ratios could be explained. © 2023, Indian Academy of Sciences.
Interstellar branched chain molecules: A theoretical-rotational study
(Springer, 2023) Satyam Srivastav; Akant Vats; Anshika Pandey; Amit Pathak
Interstellar detection of the straight-chain (n-propyl cyanide, n-C3H7CN) and branched-chain (i-propyl cyanide, i-C3H7CN) molecules toward the star-forming region, Sagittarius B2(N2) (Sgr B2(N2)) has attracted attention to study the formation mechanism and chemical evolution of branched carbon-chain molecules. These molecules are the precursors of biologically relevant prebiotic molecules, i.e., amino acids. In this light, we consider n-butyl cyanide and higher-order branched chain molecule, t-butyl cyanide from the C5H9N isomeric group. Quantum chemical calculations, such as rotational constants, dipole moments and other spectroscopic information will assist to study the chemical evolution and examine the possibility of detecting higher-order branched-chain molecules in high-mass star-forming regions. © 2023, Indian Academy of Sciences.
Interstellar dehydrogenated PAH anions: Vibrational spectra
(Oxford University Press, 2018) Mridusmita Buragohain; Amit Pathak; Peter Sarre; Nand Kishor Gour
Interstellar polycyclic aromatic hydrocarbon (PAH) molecules exist in diverse forms depending on the local physical environment. Formation of ionized PAHs (anions and cations) is favourable in the extreme conditions of the interstellar medium (ISM). Besides in their pure form, PAHs are also likely to exist in substituted forms; for example, PAHs with functional groups, dehydrogenated PAHs etc. A dehydrogenated PAH molecule might subsequently form fullerenes in the ISM as a result of ongoing chemical processes. This work presents a density functional theory (DFT) calculation on dehydrogenated PAH anions to explore the infrared emission spectra of these molecules and discuss any possible contribution towards observed IR features in the ISM. The results suggest that dehydrogenated PAH anions might be significantly contributing to the 3.3 μm region. Spectroscopic features unique to dehydrogenated PAH anions are highlighted that may be used for their possible identification in the ISM. A comparison has also been made to see the size effect on spectra of these PAHs. © 2017 The Author(s).