To have any chance of capturing the more powerful ghosts you will need better gear and it is not until you reach at least level 3 and go through the prologue section of the game's Story mode that you will be able to start improving your Particle Thrower and the other equipment you may have.
To access your equipment menu first tap on the Ghostbusters logo that is at the bottom of the main game screen and then choose 'Characters and Euipment'. If you then select the 'Equipment' menu you will be able to tap on pieces of gear you have already unlocked and press the 'Research' button to view all the possible upgrades for that item.
To perform the actual research and upgrade pieces of your equipment costs coins and also takes a specified amount of time before the process completes. At the 'Equipment' menu you will also be able to perform research to craft additional traps or ammunition. If you want to skip the timer and not have to wait for the research to complete you can do so by using Gems which is the game's premium currency.