Reactions Forming NF in Specific Electronic States

In the following, the radical in its X 2 , a A, and b 2 state is occasionally abbreviated as NF(X), NF(a), and NF(b). The symbol t denotes vibrational excitation. The radical in another excited state, c n, was recently formed from the dissociative charge-transfer reaction of He with NF3 [51]. 

The reaction of H (or D) atoms with NF2 has usually been used as a source for predominantly NF(a) and thus as a basis for various studies of NF(a) properties. For the NF2+ H reaction the following reaction channels are expected [17]  

For the determination of ki, the intensity of the infrared chemiluminescence from HF (v 1) was monitored as a function of the reagent flow at 300 K in a fast-flow, low-concentration, flowing afterglow apparatus. Comparison of the HF(v) emission intensity to that of HCl(v) from the H + CI2 reaction yielded the rate constant 3.8 x 10 cm -molecule -s for the formation of HF(v 1) (based on k = 2.06x10 cm molecule -s for H + CI2). The value had to be increased by a factor of about 3 to allow for HF(v = 0) formation, thus 1.3x10 cm -molecule s (uncertainty 50%) [17]. By measuring the decay of the hydrogen atomic resonance fluorescence under pseudo-first-order conditions (mean ratio [NF2]o/[H]o=11.3) at T=298, 421, 471, and 550 K, the rate constant kf = (i.5 + 0.2)x 10 cm -molecule s and an Arrhenius expression forT = 298 to 550 K, k = (1.9 0.5)x 10 exp[-(30 50)AT], were obtained [18]. 

NF(a A). One hypothesis supposed an initial formation of NF(X) and subsequent collisional excitation to NF(a) or NF(b) by some unknown species [22]. Later, the rapid H + NF2 (or D + NFg) reaction was proposed to lead mainly, if not exclusively, to NF(a) radicals according to reaction (1 b) [23]. Considering the Wigner-Witmer spin conservation rules [24], process (1 b) must be an addition-elimination reaction probably proceeding through a singlet-state intermediate, NHF2( A). Direct abstraction is expected for process (1 a), that is, attack of the H atom on one of the F atoms [21,23]. 

The production of NF(a) with a branching ratio 0.9 was demonstrated by two independent methods (A) Atomic resonance-fluorescence was used in a discharge flow system to study the concentration profiles of ground state NC S°) and excited state N(2p°) atoms which had 

---