N2 W 3Δu–A 3Σ+u emission in the near-infrared luminescence spectrum of N2-doped solid argon and krypton

The near-infrared emission spectrum of N2 diluted in rare-gas matrices exhibits a variety of new emission lines featuring different linewidths and decay times. One vibrational v″ progression of lines characterized by widths of 25 cm−1 and by decay times of 70 μs in Ar and of 60 μs in Kr is assigned to the forbidden electronic transition W 3Δu (v′)–A 3∑+u (v″=0–4). Selectively unrelaxed initial states v′=4 in 14N2 and v′=3 in 15N2 are observed, and the resistance of these particular levels against radiationless relaxation is attributed to bottlenecks in the cascade of internal conversion processes among the vibrational levels of the A, B, B′, and W electronic states. The assignments are based on isotope shift measurements and on quantitative estimates of allowed and induced vibrational and electronic radiative transition probabilities. The relative efficiency of multiphonon relaxation in different rare-gas matrices is discussed in the light of these and of other comparable measurements.