I use the spectroscopic information contained in quantum transition of rotational states of gas molecules to study the gas kinematics in the molecular clouds that are thousands of light years away. Different gas traces different regions of the molecular cloud. For e.g., I use ammonia transitions to trace the very dense central regions of a cloud, also known as cores and carbon monoxide transitions to study more diffuse regions of the cloud. These transitions contain kinematic information, such as velocity of clouds and dispersion velocity, which I decipher using different analyzing techniques. I am studying such motions in the Perseus molecular cloud where I am using the hyperfine splitting lines of ammonia to investigate the cloud density. Similarly, I used separate transition levels of ammonia to correctly estimate the temperature of the cloud. Further, I use the measured velocity dispersion to estimate the contribution of non-thermal motions to sustain hydrostatic equilibrium and gas infall at the center of dense core. I find that the non-thermal motions of ammonia are less than the thermal motion in most of the regions. These motions imply that the transition from supersonic turbulent motions to sub-sonic motions take place at a larger scale. I also test the thermal and nonthermal fragmentation model at the scales of dense cores.