Modelling anharmonic spectra of Polycyclic Aromatic Hydrocarbons at high temperatures
Date Issued
2020
Author(s)
Abstract
Anharmonicity plays a crucial role in determining the band profile and position of the interstellar Polycyclic Aromatic Hydrocarbons. Here we modeled the infrared spectrum of pyrene (C16H10) using \textrm{ab initio} simulations. We used our new AnharmoniCaOs code to describe the detailed structures of hot band transitions up to moderately high temperatures (600K), using Monte Carlo sampling of the states but beyond that due to high computational cost it is difficult to extend such fancy calculation up to very high temperature relevant for astrophysics. IR spectra of C16H10 beyond 600K was calculated using Density functional based tight binding molecular dynamics simulation. A gradual red shift of the band position and increasing band width is observed with increasing temperatures. The band positions at different temperatures were fitted with a linear regression and the anharmonicity factors were retrieved from the linear fits. Theoretical anharmonicity factors were compared to the recent laboratory results and previous gas phase analyses.
This is an extension of a previous project, aimed at completing the calculations to obtain (relatively) high temperature anharmonic vibrational spectra of the pyrene (C16H10) Polycyclic Aromatic Hydrocarbon, using our AnharmoniCaOs code to describe the detailed structures of hot band transitions. We achieved our scientific goal, but the calculation was significantly more demanding than anticipated. The results have been submitted to the Journal of Molecular Spectroscopy by Chakraborty et al., I here describe the technical challenges we faced and the improvements we plan to overcome or mitigate them....
Issn Identifier
0037-8720
Ads BibCode
2020MmSAI..91..291M
Rights
open.access
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