Collisional dynamics of NC4NH+ with H2 in the interstellar medium Pooja Chahal, T J Dhilip Kumar Monthly Notices of the Royal Astronomical Society, 2026 The present work explores the quantum dynamics of protonated dicyanoacetylene (NC$_4$NH$^+$) in collision with both para and ortho-H$_2$ over the temperature range 1–100 K. Such low-temperature collisions help determine the state-to-state rate coefficients for the rotational transitions of NC$_4$NH$^+$, a recently detected species in TMC-1. To study these collisions, a four-dimensional (4D) ab initio potential energy surface (PES) for the NC$_4$NH$^+$–H$_2$ system was developed using the CCSD(T)–F12b method with an augmented correlation consistent polarized triple-zeta basis set under the rigid-rotor approximation. The PES was then augmented through a neural network (NN) fitting approach to get the dense data. It was further expanded in bispherical harmonics, for the radial coefficients to be expressed in analytical form. Based on these radial coefficients, state-to-state cross-sections and rate coefficients were calculated using the exact close-coupling method for the rotational states considering to both para and ortho-H$_2$. For rate coefficients it is observed that a strong propensity is favored for even transitions over the odd ones. The resulting rate coefficients would also help model the abundance of NC$_4$NH$^+$ in the interstellar medium under non - local thermodynamic equilibrium conditions.
Photocatalytic Approach Towards Benzimidazole Synthesis and Oxidation of Indoles by Porphyrins Anu Janaagal, Ashmita Jain, Prisha Maru, Pooja Chahal, T.J.D. Kumar, Iti Gupta Chemistry an Asian Journal, 2025 This work is focused on the photocatalytic applications of three porphyrins having electron‐withdrawing and electron‐donating groups at their meso‐positions. Porphyrins were tested for the diamine coupling reaction and chemoselective oxidation of indole derivatives under visible light. The porphyrin with meso‐tetrakis‐p‐cyanophenyl groups found to be the best photoredox catalyst as compared to the rest of them. For diamine coupling, the method utilizes 0.25 mol% of the porphyrin catalyst and wide variety of aldehydes and diamine were converted to benzimidazole derivatives in high yields (up to 99%). Computational studies were done to optimize the geometry of porphyrin catalysts and provide mechanistic support for the benzimidazole synthesis. Also, oxidation of indole derivatives was achieved in decent to high yields (up to 90%) with just 0.1 mol% of porphyrin, demonstrating the traits of an efficient, and versatile photocatalyst for organic transformations.
Quantum Scattering Study of NCCNH+-H2 Collision Under Interstellar Conditions Apoorv Kushwaha, Pooja Chahal, T. J. Dhilip Kumar Journal of Computational Chemistry, 2025 The rotational dynamics of protonated cyanogen (NCCNH + ) is studied for collision with both para ( p ‐) and ortho ( o ‐) hydrogen (H 2 ) in the temperature range K. Such cold collisions with H 2 are essential to get state‐to‐state rate coefficients for rotational transitions of newly detected NCCNH + . First, the ab initio 4D potential energy surface (PES) for NCCNH + ‐H 2 collision is generated at CCSD(T)‐F12b level of theory using augmented triple zeta basis, considering rigid rotor approximation. The 4D PES is further fitted into a neural network (NN) model to augment the PES by folds. The PES is then expanded using bispherical harmonics functions to get radial terms, which are expressed as analytic functions. The cross‐sections and rate coefficients for NCCNH + are calculated using the exact close‐coupling method for rotational states up to , considering both p‐ and o‐ H 2 collisions. The rates show similar behavior to the earlier studied NCCN‐H 2 collision, with the latter having larger rate coefficients.
Quantum state-resolved rotational scattering of C5H+ by H2 in the interstellar medium Pooja Chahal, T. J. Dhilip Kumar Journal of Chemical Physics, 2025 The interstellar medium (ISM) is a complex and dynamic environment in which molecular collisions play a crucial role. Among these, protonated carbon chains are of great interest due to the presence of a permanent dipole moment and their relevance in describing astrochemical processes, making their detection possible in cold molecular clouds such as TMC-1. C5H+ (1Σg+) is an important molecule for understanding the formation and evolution of carbon-rich environments. However, to accurately model its abundance and spectroscopic properties, it is essential to account for its collisional interactions with H2, the most abundant molecule in the ISM. In this study, we present a quantum dynamical study for the C5H+–H2 collision, employing high-level CCSD(T)-F12a/aug-cc-pVTZ calculations to construct an accurate potential energy surface (PES). The PES is further augmented using a neural network fitting model, ensuring spectroscopic accuracy. The PES is expanded into radial components using bispherical harmonics. Then, close coupling methods were used to calculate cross sections and rate coefficients for different rotational transitions of C5H+, up to 100 K. Throughout the temperature range, a propensity is observed for even transitions over odd transitions. The rate coefficients for He and H2 collisions are compared for C5H+, C5, and C6H−. For both low and high temperatures, rate coefficients for C5H+ are found to be higher than C5 and C6H− for both the He and H2 collisions.
Collisional Dynamics of Newly Detected Protonated Dicyanoacetylene (NC4NH+ With He at Low Interstellar Temperatures Pooja Chahal, T. J. Dhilip Kumar Journal of Computational Chemistry, 2025 Cyanopolyyne and protonated‐dicyanopolyyne molecules always get special attention for their detection in the interstellar medium. The rotational quantum dynamics for the collision of recently detected protonated dicyanoacetylene () with He is studied to get the inelastic rate coefficients till temperature range of 100 K. An accurate potential energy surface (PES), computed using ab initio methods, has been developed for the –He collision system. The PES was developed with the coupled cluster, that is, the CCSD(T)‐F12b method in combination with the aug‐cc‐pVTZ basis set. The 2D PES has a global minimum with a value of −239.19 . The analytical fitting of this 2D PES is done to obtain the radial coefficients, that give cross‐sections for molecule till collisional energy range of 300 . The rate coefficients are achieved for the first 20 rotational transitions. An important trend is observed when comparing the de‐excitation rate coefficients at different temperatures. For transitions below , a preference for odd values is evident, which can be attributed to the anisotropy in the PES of the –He collision. This similar behavior is observed for –He collision. However, for higher transitions, a strong propensity for even transitions emerges. The results obtained in the present work will enable us to estimate the abundance of in the ISM under non‐local thermal equilibrium conditions.
Excess thermodynamics properties of binary mixtures of triacetin with cyclic and acyclic alcohols Pooja Chahal, Rajesh K. Siwach, Meena Bhandari, Sunita Rani Physics and Chemistry of Liquids, 2025 Densities, (ρ) and speeds of sound, (u) were measured for mixtures of an ester, triacetin with acyclic alcohols (tert-amyl alcohol, pentan-1-ol), and cyclic alcohols (cyclohexanol, cyclopentanol) over the temperature range of T = 298.15–318.15 K, at an interval of 5 K covering whole-mole fraction range of mixtures. The values of densities and speeds of sound at different temperatures were used to find Excess molar volumes, VEand Excess isentropic compressibilities (KSE). Furthermore, these calculated excess thermodynamic properties (VE and KSE) were fitted into the Redlich-Kister equation. Excess thermodynamic properties were further used to interpret the interactions between the components of each mixture.
Quantum rotational dynamics of linear C5 at low interstellar temperatures for H2 collision Pooja Chahal, Apoorv Kushwaha, T. J. Dhilip Kumar Journal of Chemical Physics, 2024 The quantum dynamics of carbon chains through H2 and He collisions in the interstellar medium (ISM) is an important step toward accurate modeling of their abundance in non-local thermodynamic equilibrium conditions. The C5(Σg+1) molecule is the longest pure carbon chain detected in the ISM to date. While He collisions are computationally easy to perform, the collision with much more abundant H2 is both complicated and computationally demanding. Using templates for approximating p-H2 collisional rates, such as scaling He rates and using a reduced 4D → 2D potential energy surface (PES), has limited applicability. On the other hand, any such approximation does not exist for o-H2. Therefore, a full rotational dynamics of C5 with both p- and o-H2 is performed considering both molecules as rigid-rotors. The PES is calculated using CCSD(T)-F12a/AVTZ, and a neural network fitting model has been carefully chosen to strictly obey spectroscopic accuracy and augment the PES. The augmented PES is then expanded into radial terms using the bispherical harmonics function, and close coupling calculations have been done to get the cross sections and, subsequently, rate coefficients for various rotational transitions of C5.
Inelastic scattering of PO+ by H2 at interstellar temperatures Pooja Chahal, Apoorv Kushwaha, T J Dhilip Kumar Monthly Notices of the Royal Astronomical Society, 2024 Phosphorous species are of great interest in interstellar chemistry since they are the basic blocks for building life here on Earth. Modelling the abundance and environment of recently detected PO$^{+}$ under non-local thermodynamic equilibrium (LTE) requires rotational spectra of the molecule along with accurate collisional rates with the most abundant species, hydrogen and helium. A new 4D ab initio potential energy surface (PES) of PO$^{+}$ – H$_{2}$ collision is calculated using CCSD(T)/CBS(DTQ) methodology considering rigid rotor approximation. The region containing the minima of the PES is augmented using neural networks (NNs) model while very high potentials ($\\gt 2500$ cm$^{-1}$) and asymptotic region have been approximated using Slater and R$^{-4}$ functions, respectively. The close coupling calculations have been performed using molscat software for both ortho and para-H$_{2}$. The rate coefficients have been reported for transitions $j-j^{\\prime }=$$1-0$, $2-1$, $3-2$, and $5-4$ through which PO$^{+}$ has been experimentally detected in interstellar medium (ISM). The rate coefficients for even and odd transitions of PO$^{+}$ with para-H$_{2}$ are compared with that of helium and are found to be 1.1–2.0 times higher. For even transitions ($\\Delta j = 2$), the ortho-H$_{2}$ rates are 10 per cent higher than para-H$_{2}$ rates. However, the trend reverses in the case of odd transitions ($\\Delta j = 1$) when higher J transitions are considered at low temperatures. At higher temperatures, the ortho rates cross the para-H$_{2}$ rates and become larger than the latter. The new rate coefficients with both ortho and para-H$_{2}$ will enable accurate modelling of the PO$^{+}$ abundance in the ISM under non-LTE conditions.
Rotational dynamics of CNCN by p-H2 and o-H2 collision at interstellar temperatures Apoorv Kushwaha, Pooja Chahal, T. J. Dhilip Kumar Journal of Chemical Physics, 2024 The rotational dynamics of isocyanogen (CNCN) is studied for its collision with para (p-) and ortho (o-) hydrogen (H2) in the temperature range of 1–100 K. These temperatures correspond to the cold dense molecular clouds in the interstellar medium where molecular hydrogen is the primary collider. An ab initio 4D potential energy surface (PES) is constructed keeping the two molecules under rigid rotor approximation. The PES is generated using the CCSD(T)-F12b/AVTZ level of theory. The 4D PES is further fitted into a neural network (NN) model, which can augment the surface and account for missing data points within spectroscopic accuracy. This NN-fitted PES is then expanded over a bispherical harmonics function to get radial terms, which are expressed into analytic functions. Thereafter, the cross sections (σ) are computed for rotational transitions of CNCN (j → j′) using the close-coupling and centrifugal sudden methods for both p-H2 (jc = 0) and o-H2 (jc = 1) collision till 194 cm−1. In addition, p-H2 (jc = 0, 2) cross sections are also computed using the centrifugal sudden approximation method. The collisional rates are achieved by taking the Boltzmann distribution of σ over the translational energy of H2 till 100 K. Finally, the CNCN–H2 rates are compared to CNCN–He and NCCN–H2 collisional rates. Comparing even and odd transitions for the CNCN–H2 rates show a propensity toward higher rates for even transitions especially for o-H2 collisions considering low-order transitions.
