A fluorescence model of the C₃radical in comets

Abstract

Abstract. Theoretical resonance fluorescence calculations are presented of the triatomic C3 radical and are compared with observations of the C3 emission in comets Hale-Bopp and de Vico. A theoretical model of the C3 vibration-rotational structure in theThe model takes into account the detailed structure of the bending mode ν2 which is responsible for the emission of the 4050Å group. A total of 1959 levels are considered, with 515 levels in the ground state. The main effort is to model high-resolution spectra of the 4050Å emission in comets C/1995 O1 Hale-Bopp and 122P/1995 S1 de Vico. The agreement between observed and theoretical spectra is good for a value of the dipole moment derivative of dµ dr ≈ 2.5 DebyeÅ −1 . The modeled C3 emission exhibits a pronounced Swings effect.

Long- and Short-Term Photometric Behavior of Comet Hyakutake (1996 B2)

“…However, more recent determinations of the oscillator strength of the C 3 band (cf. Rousselot et al 2001) are very close to the value originally adopted by A'Hearn. Therefore, rather than altering the fluorescence efficiency to force the same final abundances and production rates, we have, instead, kept the original value of 1 × 10 −12 erg s −1 molecule −1 resulting in a large increase (2.09×) in the derived C 3 abundance.…”

Photochemistry of C3Hphydrocarbons in Titan’s stratosphere revisited

“…Carbon atoms are indeed efficiently produced by both the H + CH (van Harrevelt et al 2002) and the N + CN (Daranlot et al 2012) reactions, whereas they are only very slowly consumed by their reaction with N 2 (Husain & Kirsch 1971) and do not react at all with CH 4 (Husain & Kirsch 1971;Kim et al 2003). As a result, the C + C 2 H 2 (along with C + C 2 H 4 ) reaction is an efficient source of C 3 H p species, such as C 3 , a very stable bi-carbene molecule found to be abundant in various interstellar media (Oka et al 2003;Mookerjea et al 2010) and in comets (Huggins 1881;Rousselot et al 2001), but absent from any current models of Titan's atmosphere. In the present study, we continue our systematic approach to improve the neutral chemical scheme of Titan's atmosphere, focusing specifically on C 3 -hydrocarbons.…”

The changing rotational excitation of C3 in comet 9P/Tempel 1 during Deep Impact

“…The 5100Å Swan bands of C 2 are also recorded in the publicly available Keck spectra, which together with models such as those of Gredel et al (1989) and Rousselot et al (2001) could be used to quantitatively compare the excitation profiles of both C 2 and C 3 . Such an analysis would also provide a constraint on chemical models of carbon-bearing molecules in comets, since variations in the formation mechanism of C 3 can change the excitation temperature.…”

“…Rousselot et al (2001) describe a statistical equilibrium model that can be used to interpret the rotationally-resolved emission spectrum of cometary C 3 by taking into account changes in heliocentric velocities and distances. However, changes in those values are small on the timescale of these observations and we assume a simple thermal distribution of states to model the emission spectrum.…”