Experimental study on rotational temperatures in nitrogen molecular beam

Rotational energy distribution in a nitrogen molecular beam was experimentally studied by (2+2) N ₂-REMPI(Resonantly Enhanced Multiphoton Ionization). REMPI is known to have high detection sensitivity, which allows obtaining the signal under the very low number density condition like a molecular beam, successfully. Obtained REMPI spectrum was fitted by a theoretical spectrum to determine rotational temperature. The spectrum was well fitted, showing the rotational energy distribution obeyed the equilibrium Boltzmann distribution. The rotational temperature in a molecular beam must be similar to the frozen rotational temperature in a free jet, since a free jet is used as a beam source in the Kantrowitz-Grey type. The parameter p ₀d, which is a product of the source pressure p ₀ and the orifice diameter d, is known to characterize a free jet. Therefore, the rotational temperature in a molecular beam was analyzed in terms of the parameter p ₀d. The rotational temperature was able to be described by the power of the parameter p ₀d. The rotational temperature and the obtained function were compared with the value in literatures, which showed good agreement.