TOWARD UNDERSTANDING CHEMICAL EVOLUTION ALONG PROTOPLANETARY DISK FORMATION

Star and planet formation is one of the most fundamental structure-formation processes in the Universe. Physical processes of star and planet formation have widely been investigated as one of the major targets of observational astronomy and astrophysics during the last few decades. Meanwhile, star and planet formation is inevitably accompanied with the evolution of interstellar matter. Increasing observational sensitivity allows us to identify about 200 interstellar molecules so far. This indicates high chemical complexity of interstellar clouds and star-forming regions despite their extreme physical condition of low temperature (10-100 K) and low density (10$^{2}$-10$^{7}$ cm$^{-3}$). Such chemical complexity would ultimately be related to an origin of a huge variety of substances in the Solar System. Thus, both physical and chemical approaches are indispensable to bridge star/planet formation studies and the Solar System science. In the last two decades, it is clearly demonstrated that envelopes and disks around solar-type protostars have significant chemical diversity: some sources harbor various saturated-"complex"-organic molecules (COMs) such as HCOOCH$_{3}$ and (CH$_{3}$)$_{2}$O, whereas some others harbor unsaturated species instead. The chemical diversity would originate from different duration time of the starless core phase of each protostar. In fact, sources showing intermediate-type of chemistry have also been found. On the other hand, the most interesting issue to be studied is how the chemical diversity in the protostellar envelopes/disks is brought into the later stages toward protoplanetary disks. Fortunately, such studies are now feasible with high sensitivity and angular-resolution capabilities of ALMA (Atacama Large Millimeter/Submillimeter Array). During its 7 year/cycle operation, spectacular images are being obtained after another by ALMA. These results have newly reminded us of a lack of sufficient information on molecular properties, such as accurate rest frequencies of molecular lines, desorption mechanism of molecules, isotopic fractionations of molecules, and so on. Modern importance of molecular science in relation to astronomy will be discussed by introducing recent observations with ALMA