We present high-angular resolution sub-millimeter continuum images and molecular line spectra obtained with the Submillimeter Array toward two massive cores that lie within Infrared Dark Clouds; one actively star-forming (G034.43+00.24 MM1) and the other more quiescent (G028.53−00.25 MM1). The high-angular resolution sub-millimeter continuum image of G034.43+00.24 MM1 reveals a compact ( ∼ 0.03 pc) and massive (∼ 29M⊙) structure while the molecular line spectrum shows emission from numerous complex molecules. Such a rich molecular line spectrum from a compact region indicates that G034.43+00.24 MM1 contains a hot molecular core, an early stage in the formation of a high-mass protostar. Moreover, the velocity structure of its 13 CO(3–2) emission indicates that this B0 protostar may be surrounded by a rotating circumstellar envelope. In contrast, the sub-millimeter continuum image of G028.53−00.25 MM1 reveals three compact ( � 0.06 pc), massive (9– 21M⊙) condensations but with no lines detected in its spectrum. We suggest that the core G028.53−00.25 MM1 is in a very early stage in the high-mass starformation process; its size and mass are sufficient to form at least one high-mass star, yet it shows no signs of localized heating. Because the combination of high – 2 – velocity line wings with a large IR–mm bolometric luminosity ( ∼ 10 2 L⊙) indicates that this core has already begun to form accreting protostars, we speculate that the condensations may be in the early phase of accretion and may eventually become high-mass protostars. We, therefore, have found the possible existence of two high-mass star-forming cores; one in a very early phase of star-formation and one in the later hot core phase. Together the properties of these two cores support the idea that the earliest stages of high-mass star-formation occur withi
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