Towards a reliable prediction of the infrared spectra of cosmic fullerenes and their derivatives in the JWST era

Abstract

Fullerenes, including C60, C70, and C60+, are widespread in space through their characteristic infrared vibrational features (C60+ also reveals its presence in the interstellar medium through its electronic transitions) and offer great insights into the carbon chemistry and stellar evolution. The potential existence of fullerene-related species in space has long been speculated and recently put forward by a set of laboratory experiments of C60+, C60H+, C60O+, C60OH+, C70H+, and [C60-Metal]+ complexes. The advent of the James Webb Space Telescope (JWST) provides a unique opportunity to search for these fullerene-related species in space. To facilitate JWST search, analysis, and interpretation, an accurate knowledge of their vibrational properties is essential. Here, we compile a VibFullerene database and conduct a systematic theoretical study on those species. We derive a set of range-specific scaling factors for vibrational frequencies, to account for the deficiency of density functional theory calculations in predicting the accurate frequencies. Scaling factors with low root-mean-square and median errors for the frequencies are obtained, and their performance is evaluated, from which the best-performing methods are recommended for calculating the infrared spectra of fullerene derivatives which balance the accuracy and computational cost. Finally, the recommended vibrational frequencies and intensities of fullerene derivatives are presented for future JWST detection.

Multifacets of Fullerene–Metal Clusters: From Fundamental to Application

“…To facilitate potential future searches, analyses, and interpretations of these fullerene-derived species in space by the James Webb Space Telescope (JWST), which has high resolution and high sensitivity in the 4.9−28.3 μm spectral range, we listed all of the scaled harmonic frequencies and corresponding transition intensities of these fullerene derivatives for their potential detection (see Table 4 in ref 46). Definitive confirmation of a specific species in space via these frequencies, however, is challenging because of the potential coincidence of infrared features from different species in addition to the possibility that some band features are hidden within broad infrared emission plateaus.…”

Metallofullerenes as potential candidates for the explanation of astrophysical phenomena

“…To possibly tackle this problem, scaling factors could be developed to make the calculated harmonic frequencies closely resemble the laboratory data. In this regard, Xu et al recently compiled a VibFullerene database that includes all the so far experimentally measured infrared frequencies of fullerene-related species, 71 They carried out a systematic theoretical study on these species using several popular density functional theory methods. Following a least-square fitting procedure by minimizing the root mean square error (RMSE), they derived a set of range-specific scaling factors for vibrational frequencies (Table 1).…”

“…In this regard, Xu et al recently compiled a VibFullerene database that includes all the so far experimentally measured infrared frequencies of fullerene-related species, including C 60 , C 70 , C 60 + , C 60 O + , C 60 OH + , C 60 H + , and C 70 H + , with totally 92 vibrational frequencies. 71 They carried out a systematic theoretical study on these species using several popular density functional theory methods. Following a least-square fitting procedure by minimizing the root mean square error (RMSE), they derived a set of range-specific scaling factors for vibrational frequencies (Table 1).…”

“…To facilitate the potential search, analysis, and interpretation of these fullerene-related species, like metallofullerenes, in space, they summarized all the scaled harmonic frequencies (see Table 4 in ref. 71). However, the conclusive identification of specific species in space remains challenging due to the potential coincidence of band features from different species or their concealment within the broad emission plateaus.…”

“…Scaling factors obtained for several different functionals with the 6-31G** basis set. Extracted from ref 71. …”