The ion-molecule reactions play a key role in the gas-phase chemistry of cold interstellar clouds. Chemical reaction network models have been successful in understanding the chemical abundance of the clouds assuming the rate constants of these reactions have more or less the same Arrhenius-like temperature dependence at cryogenic temperatures around 10 K. However, recent studies have shown that some of the ion-molecule reactions exhibit a characteristic temperature at intermediate temperatures around 10-300 K. At these temperatures, the shape of reaction barriers has a significant effect on the reaction probability and branching ratio between reaction paths. Therefore, to understand the complex gas-phase chemistry of the warm clouds in the planet-forming regions, we are keen to develop a new chemical model beyond the conventional methods limited to the cryogenic environments. The gas-phase experiment group (A04) will experimentally investigate the rate constants and their temperature dependence of important ion-neutral reactions at intermediate temperatures around 10-300 K. Taking advantage of the state-of-the-art particle beam technologies, we will develop novel experimental studies in three subgroups, the merged-beam, the ion trap, and the drift tube experiments. We will put focus on the critical subjects; (1) reaction rates of chemically active species (neutral atoms and polar molecules) and their temperature dependence, (2) the reaction branching ratios involving structural isomers, and (3) the isotope effects in the above reactions. By understanding the elementary processes of the gas-phase atomic and molecular reactions, we will explore the chemistry of the planet-forming region in collaboration with the theoretical and observational groups.