The spatial distribution of major electrical kinetic and optical parameters of a hydrogen discharge plasma with monoplasmatron geometry is measured. The data obtained were used as a basis for an analysis of the population and deactivation kinetics of atomic states with principal quantum numbers n = 3 to 6. It is established that quenching of excited atoms upon their collisions with molecules is an efficient channel for deactivating the above states. A comparison of the effective quenching cross sections obtained in the present work with the available literature data makes it possible to propose a mechanism of quenching of highly excited atoms upon their collisions with vibrationally-excited molecules. The effective cross sections of these processes are found for levels with n = 5 and 6.