Infrared chemiluminescence and energy partitioning from reactions of fluorine atoms with hydrides of carbon, silicon, oxygen, sulfur, nitrogen, and phosphorus

Abstract

The HF† infrared chemiluminescence from the reactions of fluorine atoms with PH3, SiH4, H2O, H2O2, H2S, NH3, N2H4, and three additional carbon compounds, (CH3)2O, (CH3)2S, and (CH3)3N, was studied in the same way as described in the preceding paper. With the exceptions of the N2H4 reaction, a large fraction of the energy, ≳ 45%, was released as vibrational energy of the HF† product, and population inversions were frequently found. The strong chemical interaction between HF† and NH3, (CH3)3N, N2H4, and PH3 may have led to efficient vibrational relaxation for these reactions; however, the redissociation of the adducts may give mainly HF† (v = 0), and modification of the vibrational distribution may not be severe. The results can be used to establish upper limits to some uncertain bond energies: D(SiH3–H)≤ 87 kcal mole−1; D(PH2–H)≤ 78 kcal mole−1, D(NH2–H)≤ 110 kcal mole−1 and D(N2H3–H)≤ 85 kcal mole−1. Since these F atom reactions tend to populate vibrational levels up to the maximum allowed by the thermochemistry, these limits with the exception of D(H–N2H3), which has a substantial uncertainty, probably are within 5 kcal mole−1 of the actual bond energy. Although rotational relaxation was only partially arrested, a sizeable amount of HF† rotational energy was found from the (CH3)2O, (CH3)2S, PH3, and SiH4 reactions. The (CH3)2O and (CH3)2S reactions partition more rotational energy and less vibrational energy to HF† than the reactions with most other primary C–H bonds.