We have observed the J = 3 - 2 transition of N2H and N2D to investigate the trend of deuterium fractionation with evolutionary stage in three selected regions in the infrared dark cloud (IRDC) G28.34 0.06 with the Submillimeter Telescope and the Submillimeter Array. A comprehensible enhancement of roughly 3 orders of magnitude in deuterium fractionation over the local interstellar D/H ratio is observed in all sources. In particular, our sample of massive star-forming cores in G28.34 0.06 shows a moderate decreasing trend over a factor of 3 in the N(N2D)/N(N2H) ratio with evolutionary stage, a behavior resembling that previously found in low-mass protostellar cores. This suggests a possible extension for the use of the N(N2D)/N(N2H) ratio as an evolutionary tracer to high-mass protostellar candidates. In the most evolved core, MM1, the N2H(3-2) emission appears to avoid the warm region traced by dust continuum emission and emission of 13CO sublimated from grain mantles, indicating an instant release of gas-phase CO. The majority of the N2H and N2D emission is associated with extended structures larger than 8'' (~0.2 pc).
