Nitridation at a Ti(0001)-1 × 1 surface using supersonic N 2 molecular beams was investigated by real-time photoelectron spectroscopy to clarify the adsorption reaction dynamics of N2 molecules at the Ti surface. In a whole N2 dosage region examined, N 1s spectra could be fitted well with two chemically-shifted components A and B. The binding energies were 396.9 and 396.6 eV, respectively. For both components A and B, the initial sticking probability S0, obtained by differentiating each uptake curve of N 1s, showed a decrease feature with increasing Et as the overall trend, while had significant minima at ∼0.3 and ∼1.5 eV. Such Et, dependences of S0 suggest that the chemisorbed states A and B are similarly caused by a trapping-mediated adsorption process through a physisorption state at lower Et than 0.3 eV and an activated adsorption process becomes to be dominant at higher Et than 0.3 eV. Although both components A and B can appear similarly at the initial N2 adsorption stage, the component B decreases considerably after showing a maximum. The initial increase continues, however, with changing its uptake rate for the component A, indicating a change of the nitrogen adsorption state from the component B to A with progress of nitridation.