arXiv subjects

Arghyadeb Roy

Publications and source records attributed to Arghyadeb Roy.

3 recordsLinked to original sources

arXiv2026

The impact of attenuation on cosmic-ray chemistry: I. Abundances and chemical calibrators in molecular clouds

The chemistry of shielded molecular gas is primarily driven by energetic, charged particles dubbed cosmic rays (CRs), in particular those with energies under 1 GeV. CRs ionize molecular hydrogen and helium, the latter of which contributes greatly to the destruction of molecules. CR ionization initiates a wide range of gas-phase chemistry, including pathways important for the so-called "carbon cycle", C$^+$/C/CO. Therefore, the CR ionization rate, $\zeta$, is fundamental in theoretical and observational astrochemistry. Although observational methods show a wide range of ionization rates -- varying with the environment, especially decreasing into dense clouds -- astrochemical models often assume a constant rate. To address this limitation, we employ a post-processed gas-phase chemical model of a simulated dense molecular cloud that incorporates CR energy losses within the cloud. This approach allows us to investigate changes in abundance profiles of important chemical tracers and gas temperature. Furthermore, we analyze analytical calibrators for estimating $\zeta$ in dense molecular gas that are robust when tested against a full chemical network. Additionally, we provide improved estimations of the electron fraction in dense gas for better consistency with observational data and theoretical calibrations for UV-shielded regions.

astro-ph.GA↗

arXiv2025

Binding energy distributions of alcohols, thiols, and their precursors on interstellar water ice surfaces

Binding energy (BE) is a critical parameter in astrochemical modeling, governing the retention of species on interstellar dust grains and their subsequent chemical evolution. However, conventional models often rely on single-valued BEs, overlooking the intrinsic distribution arising from diverse adsorption sites. In this study, we present BEs for monohydric alcohols, thiols, and their plausible precursors, including aldehydes and thioaldehydes. We incorporate a distribution of BEs to capture the realistic variation in adsorption strengths. The quantum chemical calculations provide a range of BE values rather than a single estimate, ensuring a more precise description of molecular diffusion and surface chemistry. The BE trend of analogous species provides qualitative insight into the dominant reaction pathways and key precursors that drive the formation of larger molecules under interstellar conditions. Oxygen-bearing species generally exhibit higher BEs than their sulfur analogues, primarily due to stronger interactions, further influencing molecular adsorption and reactivity. We implemented BE distributions in astrochemical models, revealing significant effects on predicted abundances and establishing a more accurate framework for future astrochemical modeling.

astro-ph.GA↗

arXiv2024

Assessing realistic binding energies of some essential interstellar radicals with amorphous solid water. A fully quantum chemical approach

In the absence of laboratory data, state-of-the-art quantum chemical approaches can provide estimates of the binding energy (BE) of interstellar species with grains. Without BE values, contemporary astrochemical models are compelled to utilize wild guesses, often delivering misleading information. Here, we employed a fully quantum chemical approach to estimate the BE of seven diatomic radicals - CH, NH, OH, SH, CN, NS, and NO - that play a crucial role in shaping the interstellar chemical composition, using a suitable amorphous solid water model as a substrate since water is the principal constituent of interstellar ice in dense and shielded regions. While the BEs are compatible with physisorption, the binding of CH in some sites shows chemisorption, in which a chemical bond to an oxygen atom of a water molecule is formed. While no structural change has been observed for the CN radical, it is believed that the formation of a hemibonded system between the outer layer of the water cluster and the radical is the reason for the unusually large BE in one of the binding sites considered in our study. A significantly lower BE for NO, consistent with recent calculations, is obtained, which helps explain the recently observed HONO/NH$_2$OH and HONO/HNO ratios in the low-mass hot corino IRAS 16293-2422 B with chemical models.

astro-ph.GA↗