Expected Radial Column Density of Methylcyanopolyynes in CW Leonis (IRC+10216)

Abstract

Methylcyanopolyynes (CH 3 -[C≡C] n -CN) are a particular kind of linear molecular wires, where the first three oligomers have been detected in the interstellar medium, particularly in CW Leonis (IRC + 10216), as well as in the envelopes of carbon-rich stars in a similar way to the unsubstituted cyanopolyynes. Based on the projected natural distribution in cold clouds under LTE, we have determined the radial column density of new expected methylcyanopolyynes to be present in CW Leonis (IRC + 10216). By following, we have made use of the inner molecular resistances of the internal charge transfer process presenting in these oligomeric species in order to determine the reactivity trends between them. Therefore, geometrical parameters and dipole moments determinations for these methylcyanopolyynes involving the n = 1 to 14 molecular species were obtained from Ab initio molecular orbital calculations by means of a GAUSSIAN Program, using a restricted Hartree-Fock approach and 6-311G* basis set. Our results present a similar behavior observed in cyanopolyynes, where this series reaches a saturation level at the 14th oligomer with a maximum dipole moment of 8.21 ± 0.01 (Debyes). Thus, this molecular wire model permits us to comprehend how these methylcyanopolyynes reach a maximum length in such chemical environment, in agreement to the astronomical observations and cosmological chemical models. The following CH 3 C 9 N and CH 3 C 11 N oligomers in CW Leonis should be expected near to 3.52 × 10 10 [cm 2 ] and 1.82 × 10 10 [cm 2 ], respectively.