We have calculated the capture rate coefficients for collisions of C ([sup 3]P[sub j]) and Ge ([sup 1]S[sub 0]) with unsaturated hydrocarbons and compared them with the experiments of Husain and co-workers [Clary, Haider, Husain, and Kabir, Astrophys. J. 422, 416 (1994); Husain, Ioannou, and Kabir, Z. Phys. Chemie 203, 213 (1998)]. Our findings indicate (i) that all nine electronic surfaces for the C ([sup 3]P) reactions must contribute to the observed reaction rate coefficients, (ii) a central multipole approach is inappropriate for calculating the capture rate coefficients involving the larger hydrocarbons, (iii) the trends observed in the measured rate coefficients for the Ge and C reactions can simply be understood in terms of the physical size of the hydrocarbons, and (iv) the electrostatic interaction plays a significant role in the determination of capture rate coefficients for reactions involving C ([sup 3]P) and highly polar species as well as acetylene. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]