UV fluorescence is observed in N-2 excited by VUV synchrotron radiation, with the strongest signals measured at 105.6 107.6, 109.9, and 124 mn. From the absorption spectrum we find that these are bands of the Tanaka system produced by the forbidden absorption with the transition C-3 Pi(u)(v'=0-3)<- X-1 Sigma(+)(g). The N-2 (C) state subsequently radiates to the B-3 Pi(+)(g). state producing the second positive band (2PB) fluorescence. Additional UV fluorescence is observed at excited states of Ar and CO presented as impurities in N-2 with mixing ratios of 10(-5). Similar to N-2, excited states of Ar at about 11.5 eV can be populated by resonant absorption, and then this can be followed by a collisional transfer of energy to N-2 to generate 2PB fluorescence. Among the two possible resonant states of argon, Ar*(P-1(1)) is more efficient than Ar*(P-3(1)) in producing the 2PB fluorescence through collisions. In addition, the absorption spectrum of the Lyman-Birge-Hopfield system of a(1)Pi(g)-X-1 Sigma(+)(g), and the weaker systems of B'(3)Sigma(+)(u)-X-1 Sigma(+)(g) and a' X (1)Sigma(+)(u)-X-1 Sigma(+)(g) were also observed.
