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  5. Rovibrational spectral data for several tetra-atomic silicon carbide clusters (TASCCs) are computed in this work using a CCSD(T)-F12b/cc-pCVTZ-F12 quartic force field. Accurate theoretical spectroscopic data may facilitate the observation of TASCCs in the interstellar medium which may lead to a more complete understanding of how the smallest silicon carbide (SiC) solids are formed. Such processes are essential for understanding SiC dust grain formation. Due to SiC dust prevalence in the interstellar medium, this may also shed light on subsequent planetary formation. Rhomboidal Si2C2is shown here to have a notably intense (247 km mol−1) anharmonic vibrational frequency at 988.1 cm−1(10.1 μm) forν2, falling into one of the spectral emission features typically associated with unknown infrared bands of various astronomical regions. Notable intensities are also present for several of the computed anharmonic vibrational frequencies including the cyclic forms of C4, SiC3, Si3C, and Si4. These features in the 6–10 μm range are natural targets for infrared observation with theJames Webb Space Telescope(JWST)’s MIRI instrument. Additionally,t-Si2C2,d-Si3C, andr-SiC3each possess dipole moments of greater than 2.0 D making them interesting targets for radioastronomical searches especially sinced-SiC3is already known in astrophysical media.

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  6. Dicyano-functionalized benzene and naphthalene anion derivatives exhibit a relatively rich population of electronically excited states in stark contrast to many assumptions regarding the photophysics of anions in general. The present work has quantum chemically analyzed the potential electronically excited states of closed-shell anions created by replacing hydrogen atoms with valence-bound lone pairs in benzene and naphthalene difunctionalized with combinations of -CN and -C2H. Dicyanobenzene anion derivatives can exhibit dipole-bound excited states as long as the cyano groups are not in para position to one another. This also extends to cyanoethynylbenzene anions as well as deprotonated dicyano- and cyanoethynylnaphthalene anion derivatives. Diethynyl functionalization is less consistent. While large dipole moments are created in some cases for deprotonation on the -C2H group itself, the presence of electronically excited states beyond those that are dipole-bound is less consistent. Beyond these general trends, 2-dicyanonaphthalene-34 gives strong indication for exhibiting a quadrupole-bound excited state, and the 1-cyanoethynylnaphthalene-29 and -36 anion derivatives are shown to possess as many as two valence-bound excited states and one dipole-bound excited state. These photophysical properties may have an influence on regions where polycyclic aromatic hydrocarbons are known to exist such as in various astrochemical environments or even in combustion flames. 
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