The observations of C I 1931 Å emission in the ultraviolet spectra of comets show that a large fraction of carbon atoms in the cometary coma are produced in the metastable 1D excited state. A coupled-chemistry transport model is employed to examine in detail the various processes of production and loss of the C(1D) atoms in the coma of comet 1P/Halley. Different mechanisms forming C I 1931 Å line are subsequently studied. The impacts of solar UV-EUV photons, photoelectrons, and auroral electrons of solar wind origin, on the chemistry of C(1D) and the C I 1931 Å emission are evaluated. Dissociation of CO by solar photon and electron impact are the dominant mechanisms of the production of C(1D). Contrary to the findings of the earlier works, the dissociative e-CO+ recombination is not a significant source of C(1D) in the inner (