Periodic Reporting for period 1 - ASTROCHEMISTRY (The role of pentagons in the conversion of Polycyclic Aromatic Hydrocarbons into fullerenes in the interstellar space)
Reporting period: 2022-09-01 to 2024-08-31
Summary of the context and overall objectives of the project
The project has achieved most of its objectives and milestones for the period, with relatively major improvements and additional experiments (including additional beamtime) which was achieved efficaciously within the same timeline and resources.
Scientific objectives:
As mentioned previously, the principle objective of this project was understanding the organic inventory of space and the processes that regulate their abundances by dissociation of large organic molecules. The crux of the work carried out entailed the photo-fragmentation of PAHs with the instrument for Photodynamics of PAHs (i-PoP) in the Laboratory for Astrophysics (LfA) in Leiden. The measurements performed on i-PoP at the LfA have revealed that PAHs appear to follow a universal fragmentation mechanism that gives rise to identical products, namely ionized carbon clusters in the form of cyclo[n]carbons. These end products could be the final step of the top-down breakdown processes in the photodissociation regions of the interstellar medium.
It is found that, close to stars, the abundance of C60 increases rapidly while the abundance of PAHs decreases. This has been attributed to photochemical fragmentation and isomerization processes under the influence of the strong stellar ultraviolet (UV) radiation field but the details of these processes are not yet understood. A detailed study of the bright reflection nebula, NGC 7023, has given evidence that the evolution of the profile of the mid-IR bands is related to the chemical evolution under the effect of UV photons.
Neutral and cationic C60 – identified through their unique IR and visible spectrum – are the largest molecular species identified in space. The presence of pentagons in a planar graphene-flake leads to bending of the molecular structure enabling the closure upon itself and formation of a 3D structure. , Pentagon formation is thus a key step in the photochemical transformation of PAHs into fullerenes. Spectroscopic evidence for pentagon formation upon PAH photo-dissociation has been reported in the laboratory for small PAH species, containing up to three aromatic rings. , These experiments suggest that PAHs with only hexagonal rings could be the parent molecules (Parent-PAHs) for the formation of PAHs with pentagonal ring(s) in adequate conditions. In addition, some PAHs with pentagons may be more photochemically stable than PAHs of similar size and therefore represent likely candidates for the interstellar molecular inventory. However, the photochemical evolution of PAHs with pentagons is largely unexplored and the generality of this conclusion is unknown. Given the presence of C60 in space, the likely astrochemical connection of C60 and PAHs in space, and the potential photochemical stability of pentagon containing PAHs, a focused study to improve the understanding of such species is done in my research.
Scientific objectives:
As mentioned previously, the principle objective of this project was understanding the organic inventory of space and the processes that regulate their abundances by dissociation of large organic molecules. The crux of the work carried out entailed the photo-fragmentation of PAHs with the instrument for Photodynamics of PAHs (i-PoP) in the Laboratory for Astrophysics (LfA) in Leiden. The measurements performed on i-PoP at the LfA have revealed that PAHs appear to follow a universal fragmentation mechanism that gives rise to identical products, namely ionized carbon clusters in the form of cyclo[n]carbons. These end products could be the final step of the top-down breakdown processes in the photodissociation regions of the interstellar medium.
It is found that, close to stars, the abundance of C60 increases rapidly while the abundance of PAHs decreases. This has been attributed to photochemical fragmentation and isomerization processes under the influence of the strong stellar ultraviolet (UV) radiation field but the details of these processes are not yet understood. A detailed study of the bright reflection nebula, NGC 7023, has given evidence that the evolution of the profile of the mid-IR bands is related to the chemical evolution under the effect of UV photons.
Neutral and cationic C60 – identified through their unique IR and visible spectrum – are the largest molecular species identified in space. The presence of pentagons in a planar graphene-flake leads to bending of the molecular structure enabling the closure upon itself and formation of a 3D structure. , Pentagon formation is thus a key step in the photochemical transformation of PAHs into fullerenes. Spectroscopic evidence for pentagon formation upon PAH photo-dissociation has been reported in the laboratory for small PAH species, containing up to three aromatic rings. , These experiments suggest that PAHs with only hexagonal rings could be the parent molecules (Parent-PAHs) for the formation of PAHs with pentagonal ring(s) in adequate conditions. In addition, some PAHs with pentagons may be more photochemically stable than PAHs of similar size and therefore represent likely candidates for the interstellar molecular inventory. However, the photochemical evolution of PAHs with pentagons is largely unexplored and the generality of this conclusion is unknown. Given the presence of C60 in space, the likely astrochemical connection of C60 and PAHs in space, and the potential photochemical stability of pentagon containing PAHs, a focused study to improve the understanding of such species is done in my research.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
The principle objective of this project was understanding the organic inventory of space and the processes that regulate their abundances by dissociation of large organic molecules. Within this field, the characteristics of the interstellar PAH (Polycyclic Aromatic Hydrocarbons) family and their (photochemical) relationship to fullerenes (i.e. C60) have in recent years become a focus. The purpose of this project is to carry out a systematic experimental and theoretical study on pentagon-containing PAHs and their “PAH-parent” counterparts. The specific objectives of this project was to explore the fundamental questions: (1) How do pentagons influence the photochemical stability of PAHs? (2) How do pentagons influence the IR spectral characteristics of PAHs? (3) How does the presence of pentagons influence the abundance and IR spectra in astronomically relevant environments? (4) What are their implications for the interpretation of astronomical spectra? (5) What does this tell us about the interrelationship of PAHs and C60 in space?
This project focused on larger (>20 C, >30 C) and compact PAHs that have the high photo-stability to withstand the intense UV radiations in space and hence could be present at high abundances in the ISM. Given the presence of C60 in space, the likely astrochemical connection of C60 and PAHs in space, and the potential photochemical stability of pentagon containing PAHs, a focused study of such species were carried out. This was done by both spectrometric and spectroscopic techniques, using the facility in the Leiden University and the FELIX facility respectively. The molecules studied using the i-PoP facility were (i) Corannulene, (ii) Sumanene, (iii) Truxene, and (iv) Decacyclene. Among which spectroscopy were carried out for the most astronomically important Sumanene using the cutting edge facilities at FELIX, The Netherlands. Both the projects were successful and potentially leads to three good impact publications in peer-reviewed international journals.
In fact, the project at FELIX were done more efficiently that we could add an additional project to record the infrared spectroscopy of neutral PAHs, which was also very successful and will potentially be published by early 2025. In addition, the molecular dynamics simulations of the fragmentation of PAHs were carried out in collaboration with the Prof. Alessandra Candian, University of Amsterdam which supported in the interpretation of the experimental results.
Training deliverables included an appropriate knowledge of interstellar chemistry, familiarity with all experimental methods and tools, improvement in supervision and management skills, familiarity with new techniques and experiments, becoming a Principle Investigator of experiments to be performed at the FELIX facility, Nijmegen. The projected dissemination deliverables were: (i) Two published papers, one paper from WP1 and the other from WP2, (the third paper will be prepared for submission in 2025) (ii) contributions to AstroPAH newsletter as an Editor, (iii) presentations of results in international conferences and (iv) contributions towards outreach and a popular talk. The Career development deliverables included interaction with a Leiden job coach as well as targeted laboratory visits within and outside of Europe. The final deliverables concerned the project management. These were the contract/project close-out and a risk register.
The training deliverables (WP4, WP5, WP6, and WP7) were also carried out as proposed and the experience was fruitful making me gain new collaborators, mentorship and leadership qualities, expand my frontiers in carrier, and also securing a Research Associate position.
This project focused on larger (>20 C, >30 C) and compact PAHs that have the high photo-stability to withstand the intense UV radiations in space and hence could be present at high abundances in the ISM. Given the presence of C60 in space, the likely astrochemical connection of C60 and PAHs in space, and the potential photochemical stability of pentagon containing PAHs, a focused study of such species were carried out. This was done by both spectrometric and spectroscopic techniques, using the facility in the Leiden University and the FELIX facility respectively. The molecules studied using the i-PoP facility were (i) Corannulene, (ii) Sumanene, (iii) Truxene, and (iv) Decacyclene. Among which spectroscopy were carried out for the most astronomically important Sumanene using the cutting edge facilities at FELIX, The Netherlands. Both the projects were successful and potentially leads to three good impact publications in peer-reviewed international journals.
In fact, the project at FELIX were done more efficiently that we could add an additional project to record the infrared spectroscopy of neutral PAHs, which was also very successful and will potentially be published by early 2025. In addition, the molecular dynamics simulations of the fragmentation of PAHs were carried out in collaboration with the Prof. Alessandra Candian, University of Amsterdam which supported in the interpretation of the experimental results.
Training deliverables included an appropriate knowledge of interstellar chemistry, familiarity with all experimental methods and tools, improvement in supervision and management skills, familiarity with new techniques and experiments, becoming a Principle Investigator of experiments to be performed at the FELIX facility, Nijmegen. The projected dissemination deliverables were: (i) Two published papers, one paper from WP1 and the other from WP2, (the third paper will be prepared for submission in 2025) (ii) contributions to AstroPAH newsletter as an Editor, (iii) presentations of results in international conferences and (iv) contributions towards outreach and a popular talk. The Career development deliverables included interaction with a Leiden job coach as well as targeted laboratory visits within and outside of Europe. The final deliverables concerned the project management. These were the contract/project close-out and a risk register.
The training deliverables (WP4, WP5, WP6, and WP7) were also carried out as proposed and the experience was fruitful making me gain new collaborators, mentorship and leadership qualities, expand my frontiers in carrier, and also securing a Research Associate position.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
The first objective of the research training was to expand my field of research into that of experimental astrophysics and astrochemistry, thus furthering my understanding of how laboratory experiments can be utilized to recreate and model physical and chemical processes in the interstellar medium. Beside an intense literature study, this has been effectively done over the past two years. The Leiden Observatory environment has allowed me to interact with researchers specializing in protoplanetary disks, galaxies, active galactic nuclei, exoplanets, etc. I was able to gain insight firsthand how chemistry and physical chemistry in particular are used to acquire knowledge about our universe.
The next training objective concerned the expansion of my experimental knowledge towards ion traps and PAHs. This knowledge was very effectively transferred as there was a student with two years of experience who can kick start my learning. This equipped me to perform a significant amount of measurements independently.
As a part of my third training, I was a co-organizer of LEAPS (The Leiden/ESA Astrophysics Program for Summer Students) 2023 actively playing my role: proposing a project, framing deadlines, reviewed applications, interviewing and selecting the best candidate among hundreds of international applicants, conducting scientific tours for interns, etc. I supervised a LEAPS student Adibah Nur Zainol Abidin, who was a Masters student in Applied chemistry from Malaysia. She has now successfully secured a PhD position in the University of Delft to pursue experimental Astrochemistry.
The fourth training objective was realized with my secondment to FELIX where we studied further an exotic group of PAH cations with two different techniques – (i) Laser desorption molecular beam spectroscopy (BUMA-1); and (ii) 22-pole 4 K cold trap (FELion). Gaining experience with two state of the art experimental facilities at FELIX went beyond what was proposed giving me additional benefit and learning experience within the same timeline. Not only did my experimental training include this new apparatus, but also the use of the FELIX free electron laser, how it works and proposal writing to obtain beamtime which effectively worked out and made a merit in my scientific career.
As the final training objective, I was introduced to molecular dynamics simulations using the software DemonNano which is a sophisticated higher-end computational tool to calculate and visualize the fragmentation steps of PAHs.
Impact of the Result: The impact that this fellowship has had on my career has already been immense and I estimate that in the coming years, the effect will fully materialize in obtaining a permanent position in academia. I have also secured a contract based Research Associate position at ATOMKI, Hungary for 2 years. The impact of the work carried out on a societal level is impossible to predict but is nonetheless above zero.
The newly identified breakdown products of PAHs detected in my experiments, namely C7H3+, C8H5+, C9H3+, C10H5+, C10+, C11+, etc., could potentially be the proxies to hunt for PAHs including the buckybowls (and other mid- to large-sized PAHs) in space. They have yet not been studied in detail. Their chemistry is entirely unknown and this work implies that their interstellar chemistry may be of significant importance. Not only could these molecules hold the key to the puzzle of the Diffuse Interstellar Bands, but their chemistry could lead to development of new materials with entirely unexplored characteristics.
There could be spin-offs of this project which I’m exploring at present. The spectroscopy of these molecules can indeed be performed at Prof. Stephen Schlemmer’s laboratory in the University of Cologne. I have proposed to extend this project for my future study with Prof. Schlemmer through the Humboldt Fellowship, and awaiting the result.
Moreover, the potential users of the project results are first and foremost the astronomical (astrophysical & astrochemical) community. This work had emphasized that both the buckybowls, and its photofragments are important interstellar candidates to hunt for in the coming years.
The next training objective concerned the expansion of my experimental knowledge towards ion traps and PAHs. This knowledge was very effectively transferred as there was a student with two years of experience who can kick start my learning. This equipped me to perform a significant amount of measurements independently.
As a part of my third training, I was a co-organizer of LEAPS (The Leiden/ESA Astrophysics Program for Summer Students) 2023 actively playing my role: proposing a project, framing deadlines, reviewed applications, interviewing and selecting the best candidate among hundreds of international applicants, conducting scientific tours for interns, etc. I supervised a LEAPS student Adibah Nur Zainol Abidin, who was a Masters student in Applied chemistry from Malaysia. She has now successfully secured a PhD position in the University of Delft to pursue experimental Astrochemistry.
The fourth training objective was realized with my secondment to FELIX where we studied further an exotic group of PAH cations with two different techniques – (i) Laser desorption molecular beam spectroscopy (BUMA-1); and (ii) 22-pole 4 K cold trap (FELion). Gaining experience with two state of the art experimental facilities at FELIX went beyond what was proposed giving me additional benefit and learning experience within the same timeline. Not only did my experimental training include this new apparatus, but also the use of the FELIX free electron laser, how it works and proposal writing to obtain beamtime which effectively worked out and made a merit in my scientific career.
As the final training objective, I was introduced to molecular dynamics simulations using the software DemonNano which is a sophisticated higher-end computational tool to calculate and visualize the fragmentation steps of PAHs.
Impact of the Result: The impact that this fellowship has had on my career has already been immense and I estimate that in the coming years, the effect will fully materialize in obtaining a permanent position in academia. I have also secured a contract based Research Associate position at ATOMKI, Hungary for 2 years. The impact of the work carried out on a societal level is impossible to predict but is nonetheless above zero.
The newly identified breakdown products of PAHs detected in my experiments, namely C7H3+, C8H5+, C9H3+, C10H5+, C10+, C11+, etc., could potentially be the proxies to hunt for PAHs including the buckybowls (and other mid- to large-sized PAHs) in space. They have yet not been studied in detail. Their chemistry is entirely unknown and this work implies that their interstellar chemistry may be of significant importance. Not only could these molecules hold the key to the puzzle of the Diffuse Interstellar Bands, but their chemistry could lead to development of new materials with entirely unexplored characteristics.
There could be spin-offs of this project which I’m exploring at present. The spectroscopy of these molecules can indeed be performed at Prof. Stephen Schlemmer’s laboratory in the University of Cologne. I have proposed to extend this project for my future study with Prof. Schlemmer through the Humboldt Fellowship, and awaiting the result.
Moreover, the potential users of the project results are first and foremost the astronomical (astrophysical & astrochemical) community. This work had emphasized that both the buckybowls, and its photofragments are important interstellar candidates to hunt for in the coming years.