麻豆淫院

The James Webb Space Telescope (JWST) has unlocked the depths of interstellar space with unprecedented clarity, offering humanity a high-resolution window into the cosmos. Harnessing this newfound capability, an international team of researchers set out to investigate how polycyclic aromatic hydrocarbons (PAHs)鈥攐rganic molecules and key players in cosmic chemistry鈥攕urvive the harsh conditions of space and uncover the mechanism behind their resilience.

PAHs have been spotted in cold molecular clouds, where they endure constant bombardment from high-energy ultraviolet radiation and cosmic rays. These energetic particles should not only ionize and fragment but also destroy the molecules, yet they remain intact.

A new study in 麻豆淫院ical Review Letters reports that closed-shell PAHs, such as the indenyl cation, employ a surprising survival strategy: Instead of breaking apart, they efficiently dissipate excess energy through recurrent fluorescence and infrared emission. This clever mechanism allows them to resist the extreme conditions of space far more effectively than previously believed.

PAHs are scattered in interstellar space, serving as one of the galaxy's largest reservoirs of carbon, holding up to 10%鈥�25% of the element essential for building life. These molecules have unique infrared signatures, detected using radio and infrared emission astronomy.

JWST's highly sensitive infrared data鈥攖ogether with earlier findings from the Spitzer Space Telescope鈥攈as confirmed that PAHs are widespread throughout space. Closed-shell PAHs have been detected in dark interstellar clouds, while their ionized counterparts are expected to be present in brighter, star-forming regions.

Previous laboratory experiments investigating these organic molecules have shown that radical cations of open-shell PAHs cool off their excess energy through recurrent fluorescence鈥攁 type of fluorescence that occurs when a molecule that has relaxed to a lower electronic state absorbs heat to become re-excited, then emits a photon as it returns to its ground state. These studies, however, only analyzed this phenomenon in radical species and not neutral closed-shell PAHs that the JWST observed.

For this study, the researchers focused on the indenyl cation (C鈧塇鈧団伜), a closed-shell PAH relevant to interstellar clouds. Cold interstellar conditions were simulated using DESIREE, an electrostatic ion-beam storage ring in Stockholm, which can store ions for hours at cryogenic temperatures (~13 K) and ultra-low pressures. The C鈧塇鈧団伜 ions in the ring were internally energized to mimic the conditions after energetic collisions.

The team then watched how the ions behaved鈥攄id they lose energy either by fragmenting or by radiative cooling? The collected data was then analyzed using the master equation model (theoretical modeling) and Ab initio molecular dynamics (computational chemistry technique).

The result indicated that the indenyl cation cooled down efficiently via a combination of IR emission and especially RF, even when it started with vibrational energies up to 5.85 eV, which is far above its dissociation threshold. RF was found to be the dominant cooling mechanism at high internal energies, far more effective than IR emission alone. Furthermore, experimental data matched well with the master equation model when the models included RF instead of excluding it, reinstating its importance in the radiative stabilization process.

The researchers note that their findings help explain why closed-shell PAHs are more abundant in space than expected鈥攁n insight that's essential for improving models of interstellar chemistry.

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