arXiv subjects

D. Campisi

Publications and source records attributed to D. Campisi.

3 recordsLinked to original sources

arXiv2026

Broadband spectroscopy of astrophysical ice analogues: IV. Optical constants of N$_2$ ice in the terahertz and mid-infrared ranges

Context. Understanding the optical properties of astrophysical ices is crucial for modeling dust continuum emission and radiative transfer in cold, dense interstellar environments. Molecular nitrogen (N$_2$), a major nitrogen reservoir in protoplanetary disks, plays a key role in nitrogen chemistry, yet the lack of direct terahertz (THz)--infrared (IR) optical constants for N$_2$ ice introduces uncertainties in radiative transfer models, snowline locations, and disk mass estimates. Aims. We present direct measurements of the optical properties of N$_2$ ice over a broad THz--IR spectral range using terahertz pulsed spectroscopy (TPS) and Fourier-transform infrared spectroscopy (FTIR), supported by density functional theory (DFT) calculations and comparison with literature data. Methods. N$_2$ ice was grown at cryogenic temperatures by gas-phase deposition onto a cold silicon window. The THz complex refractive index was directly reconstructed from TPS data, while the IR response was derived from FTIR measurements using Kramers--Kronig relations. The optical response was parameterized with a Lorentz dielectric model and validated by DFT calculations. Results. The complex refractive index of N$_2$ ice is quantified from $\nu = 0.3$--$16$~THz ($\lambda = 1$~mm--$18.75~\mu$m). Resonant absorption peaks at $\nu_\mathrm{L} = 1.47$ and $2.13$~THz with damping constants $\gamma_\mathrm{L} = 0.03$ and $0.22$~THz are attributed to optically active phonons of the $\alpha$-N$_2$ crystal. Conclusions. We provide a complete set of the THz--IR optical constants for \ce{N2} ice by combining TPS and FTIR spectroscopy. Our results have implications for future observational and modeling studies of protoplanetary disk evolution and planet formation.

astro-ph.EP↗

arXiv2025

Superhydrogenation of indene at low temperatures

The hydrogenation of polycyclic aromatic hydrocarbons (PAHs) is crucial to understanding molecular hydrogenation formation in the interstellar medium. This process also helps to elucidate the weakening of the aromatic bonds in PAHs, which may function as a carbon reservoir. Tunneling can significantly promote the hydrogenation process in a low to moderate temperature range. We present the hydrogenation sequence of the newly observed PAH molecule, indene, and clarify the tunneling rule at temperature in photodissociation region (PDR) and dark molecular cloud conditions. In addition, we report fit parameters to be utilized in astronomical modeling. The hydrogenation sequence was studied using simple hydrogenation rules and confirmed by barriers from density functional theory (DFT). To make our kinetic studies useful to modelers, we implemented a Monte Carlo method based program to generate and optimize random initial fit parameters (alpha, beta, gamma, and T0) to achieve the statistically best fit. We find that indene hydrogenation follows rules similar to those of other PAHs, such as pentacene, coronene, and corannulene, with binding energies for odd numbered hydrogenation steps ranging from 0.5 to 2 eV and barriers around 0.13 eV for the first, fifth, and seventh hydrogenation steps. The third hydrogenation step is the rate limiting step, similar to what is found for other PAHs. Even numbered hydrogenation steps have lower barriers and lead to more stable intermediates as a result of radical recombinations. The hydrogenation sequence follows a scheme that strongly depends on the PAH's shape, the number of aromatic rings, and the presence of five membered rings. Furthermore, we observe that tunneling plays an important role in the hydrogenation of indene at temperatures between 30 and 75 K, which corresponds to the temperatures of dust in PDRs.

astro-ph.GA↗

arXiv2024

Computational Astrochemistry Journey towards the molecular universe

In astrochemistry, computational methods play a crucial role in addressing fundamental astronomical questions. Interstellar molecules profoundly influence the chemistry and physics of the interstellar medium (ISM), playing pivotal roles in planet formation and the emergence of life. Understanding their chemistry relies on theoretical approaches such as Density Functional Theory (DFT) and post-Hartree-Fock methods, which are essential for exploring pathways to molecular complexity and determining their interstellar abundances. Various theoretical methods investigate the formation of interstellar molecules in both gaseous and solid states. Molecules in interstellar space may originate from bottom-up processes (building up from CO molecules) or top-down processes (polycyclic aromatic hydrocarbon fragmentation). Here, we present a journey of theoretical investigations aimed at studying the reactivity of interstellar molecules in space.

astro-ph.GA↗