A pulsed microwave surfaguide discharge operating at 2.45 GHz was used for the conversion of molecular nitrogen into valuable compounds in several gas mixtures: N2:O2, N2:O2:CO2 and N2:CO2. The ro-vibrational absorption bands of the molecular species were monitored by a Fourier transform infrared apparatus in the post-discharge region in order to evaluate the relative number density of species, specifically NO production. The effects of specific energy input, pulse frequency, gas flow fraction, gas admixture and gas flow rate were studied for better understanding and optimization of the NO production yield and the corresponding energy cost (EC). By both the experiment and modelling, a highest NO yield is obtained at N2:O2 (1:1) gas ratio in N2:O2 mixture. The NO yield reveals a small growth followed by saturation when pulse repetition frequency increases. The energy efficiency start decreasing after the energy input reaches about 5 eV/molec, whereas the NO yield rises steadily at the same time. The lowest EC of about 8 MJ mol−1 corresponding to the yield and the energy efficiency of about 7% and 1% are found, respectively, in an optimum discharge condition in our case.

A pulsed microwave surfaguide-type discharge used for nitrogen fixation in N[Formula: see text]–O[Formula: see text] gas mixtures is characterized by optical emission spectroscopy. Results show that both rotational and vibrational temperatures are elevated in the active zone near the waveguide, decaying along the discharge tube in both upstream and downstream. The characteristic length of optical emission from NO([Formula: see text]-[Formula: see text]) transition gets contracted when pressure increases, specifically at [Formula: see text] Torr. The degree of vibrational non-equilibrium (defined as the ratio between vibrational and rotational temperatures) is decreased by a factor of two when pressure changes from 0.6 to 10 Torr. Non-equilibrium likely disappears as the discharge pressure rises, resulting in a gas temperature elevation. A correlation between gas residence time, pulse duration, and characteristic times for different energy transfer channels is discussed. The rotational–vibrational dynamics differs for NO and N[Formula: see text] during the pulse. Both species lose vibrational excitation at the beginning of the pulse, whereas N[Formula: see text] gets re-excited again during the second half of the pulse, which may occur as a result of an efficient pumping-up effect through the vibrational–vibrational energy transfer. At the same time, vibrational relaxation of NO takes place primarily due to a strong vibrational–translational exchange via NO–O[Formula: see text] and NO–O collisions.