Optical emission and absorption spectroscopy and double Langmuir probe diagnostics have been applied to measure the plasma parameters of an expanding magnetized hydrogen plasma jet. The rotational temperature of the excited state H 2 ͑d 2 ⌸ u ) has been determined by analyzing the intensity distribution of the spectral lines of the Fulcher-␣ system of H 2 . The gas temperature in the plasma, which is twice the value of the rotational temperature is equal to Ӎ 520 K. Several clear indications of presence of the ''hot'' electrons have been observed in the plasma: ͑1͒ Langmuir probe measurements ͑T e Ӎ1.4 eV͒, ͑2͒ appearance of the Fulcher-␣ system of H 2 ͑excitation potential ⌬Eϭ13.87 eV͒, ͑3͒ low rotational temperature ͑T rot * Ӎ260 K͒ of the excited H 2 ͑d 3 ⌸ u ) molecules, ͑4͒ local excitation in the plasma of Ar I͑⌬E ϭ15.45 eV͒, and Ar II͑⌬E ϭ19.68 eV͒ spectral lines, ͑5͒ local excitation in the plasma of He I͑⌬E ϭ23.07 eV and ⌬Eϭ24.04 eV͒ spectral lines. Optical actinometry has been applied to measure the absolute density of hydrogen atoms and hydrogen dissociation degree in the plasma. The measured absolute density of hydrogen atoms are in the ͑1-1.4͒ϫ10 20 m Ϫ3 range, and the corresponding dissociation degree of the hydrogen plasma is in the range of 8%-13%.

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