Structure and electronic spectra of the C anion

Abstract

Ab initio calculations are employed for determining structures, spectroscopic parameters and transitions to the excited electronic states of the astrophysical relevant C anion, which is a potential intermediate of chemical processes involving carbon chains and polycyclic aromatic hydrocarbons. Calculations confirm the prominent stability of linear carbon chain anions which guarantees their formation. The lowest doublet potential energy surface of C displays six isomers, whereas in the lowest quartet potential energy surface, a unique minimum energy geometry is found. The most stable form is the linear anion l‐C (X2Πu) followed by the c‐C (X2A1’) at 9291 cm−1 above in energy, which presents a distorted D3h structure. The other isomers are also located at more than 9000 cm−1 above l‐C (X2Πu). For each isomer, a set of spectroscopic parameters including their equilibrium structures, rotational constants at equilibrium, harmonic wavenumbers, dipole moments and electron affinities are predicted. For linear C, eight electronic states lying below the electron detachment threshold, are computed. Four doublet electronic states, which play important roles in the C reactivity, lie below 2 eV. Spin–orbit constants for the upper electronic states of l‐C are predicted.

Theoretical Characterization of C3H and C5H and Their Anions

“…Structural isomerism is extensive in interstellar clouds (Lovas et al 2010). In previous papers (Senent & Hochlaf 2010;Massó et al 2007;Massó & Senent 2009;Hammoutène et al 2012;Al-Mogren et al 2013; Al-Mogren & Senent 2017), we focus on the large number of stable geometries of unsaturated chains containing a unique heteroatom; many of them are of very low stability. Frequently, linear forms and isomers with three-carbon cycles present noticeable stabilities.…”

Collision excitation of c-C3H−(X1A1) by He

“…The detectability of a molecular species depends on abundances, physical properties, and reactivity. [20][21][22][23][24][25][26] The mechanisms of formation of CnH − species in astrophysical environments are a common subject of many inquiries. 4,[27][28][29][30][31] The CnH radicals have a large electronic affinity, and their anions are predicted to be abundant in interstellar and circumstellar clouds.…”

Theoretical Characterization of C6N, C6N−, and C6N+

“…Our previous studies of astrophysical carbon chains (Massó et al 2007;Inostroza et al 2008;Massó & Senent 2009;Inostroza & Senent 2010;Senent & Hochlaf 2010Hammoutene et al 2012;Al-Mogren et al 2013), as well as other previous works (van Order & Saykally 1998;Jochnowitz & Maier 2008), show that unsaturated carbon clusters can display a large density of low-energy electronic states and can adopt different stable geometrical structures with peculiar electronic distribution and spin multiplicities. In the case of the relatively large C 6 N chain, which involves a unique nitrogen atom, the number of configurations is extremely large.…”

“…Since the observations of the undetected charged and neutral chains imply a detailed laboratory characterization, the aim of the present work is the study of the C 6 N species, its anions, and its cations, following the same procedure applied to C 6 (Massó & Senent 2009), -C 6 (Hammoutene et al 2012), and C 7 (Al-Mogren et al 2013). Although many previous works have been devoted to the C 6 N nitrogen-terminated linear carbon chains (Botschwina 2003(Botschwina , 1996McCarthy et al 2003;Cernicharo et al 2008), few works have attended to the nonlinear isomers and to the C 6 N isocyanates that can be stable enough to play relevant chemical roles (Chuchev & Belbruno 2002;Kostko et al 2010).…”