ARF-LASER PHOTO-DISSOCIATION OF NH3 AT 193-NM - INTERNAL ENERGY-DISTRIBUTIONS IN NH2X2B1 AND A2A1, AND 2-PHOTON GENERATION OF NH-A3-PI AND B1-SIGMA+

Ammonia is photolyzed with an ArF excimer laser at 193 nm. NH2 is formed in the Ã2A1 state, detected through the identification of Ã2A1 → X̃2B1 emission bands between 620 and 1100 nm, and also in the X̃2B1 state, identified by dye laser induced fluorescence on the à ← X̃ transition. The Ã-state yield is about 2.5% relative to the X̃-state. The Ã2A1 state has a propensity for being formed in high Ka rotational levels v2 vibrational levels of the Ã2A1 state appear to be populated in a monotonically decreasing distribution, with an average vibrational energy content of 1000 cm-1. Rotational populations are deduced for the 050 Σ vibrational level of the Ã2A1 state. The colder-than-room-temperature rotational distribution (TTDI = 210 ± 40 K) is explained by angular momentum conservation arguments. The vibrational and rotational features observed in the dye laser induced fluorescence excitation spectrum of NH2 Ã←X̃ could not be assigned at near collision-free pressures. However, under thermalized conditions, the 090 ← 000 Σ, 090 ← 000 Δ, 0 100 - 000 π and 0 100 ← 000 φ bands are clearly identified. Arguments are presented which show that the nascent X̃2B1 photofragment is created either with the v2 vibrational population, or the Ka rotational population inverted. NH A 3Π → X 3Σ- and b 1Σ+ → X 3Σ- emission are also detected at 336 and 471 nm, respectively. Formation of NH A 3Π and b 1Σ+ si attributed to two-photon resonance processes. © 1979.