The adsorption of pyridine at 200 and 300 K on single-domain Si(100)-2 x 1 surfaces at saturation coverage was investigated by means of x-ray photoelectron spectroscopy and angular-dependent near-edge x-ray adsorption fine-structure spectroscopy (NEXAFS). Spectroscopic results are compared with density functional theory calculations. The N 1(s) NEXAFS spectroscopic signatures of three chemical moieties (dative bond, C-C=N-C and Si-N sp(3)) are identified. At 200 K all surface products present Si-N bonds (dative bond and Si-N sp(3)), while at 300 K, C-C= N-C moiety is also detected probing minor species without a Si-N bond. At both temperatures the coexistence of these various species are dominated by 1,4-di-sigma butterflies (Si-N sp(3)).