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, $\text{≳ 45\%}$ , 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: $\mathrm{D(}{\mathrm{SiH}}_3\mathrm{–H}\text{)≤ 87\hspace{0.17em}}\mathrm{kcal}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}\mathrm{;\hspace{0.17em}D(}{\mathrm{PH}}_2\mathrm{–H}\text{)≤ 78\hspace{0.17em}}\mathrm{kcal}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}\mathrm{,\hspace{0.17em}D(}{\mathrm{NH}}_2\mathrm{–H}\text{)≤ 110\hspace{0.17em}}\mathrm{kcal}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}$ and $\mathrm{D(}{\mathrm{N}}_2{\mathrm{H}}_3\mathrm{–H}\text{)≤ 85\hspace{0.17em}}\mathrm{kcal}\hspace{0.17em}{\mathrm{mole}}^{\text{−1}}$ . 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.