Flash Photolytic Production, Reactive Lifetime, and Collisional Quenching of O2(b 1Σg+, υ′ = 0)

Collisional quenching of ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}=\hspace{0.17em}0)}$ at room temperature by O₂ and a variety of foreign gases has been investigated with a pulsed lifetime measurement technique. ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}=\hspace{0.17em}0)}$ has been produced in a pulsed mode through flash photolysis of O₂ in the vacuum uv and has been detected through the emission of the (0, 0) band at 7620 Å of the forbidden ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}{\mathrm{\hspace{0.17em}\to \hspace{0.17em}X}}^3{\Sigma }_g^{-}$ transition. The (0, 0) band intensity has been measured as a function of time after the photolysis flash and as a function of the O₂ and foreign gas pressures. Quenching rate constants are derived from the reactive lifetimes. The photolytic production of ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}=\hspace{0.17em}0)}$ from O₂ and the quenching by O₂ has been studied at O₂ pressures from 0.02–100 torr. The observations at low O₂ pressures from 0.02 to about 1 torr are consistent with the previously established fast ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+})$ production mechanism, $${\mathrm{O}}_2\mathrm{\hspace{0.17em}+\hspace{0.17em}h\nu \hspace{0.17em}\to \hspace{0.17em}}\mathrm{O}{(}^1\mathrm{D)\hspace{0.17em}+\hspace{0.17em}}\mathrm{O}{(}^3\mathrm{P),}$$ $$\mathrm{O}{(}^1\mathrm{D)\hspace{0.17em}+\hspace{0.17em}}{\mathrm{O}}_2{\mathrm{(X}}^3{\Sigma }_g^{-}\mathrm{)\hspace{0.17em}\to \hspace{0.17em}}\mathrm{O}{(}^3\mathrm{P)\hspace{0.17em}+\hspace{0.17em}}{\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\mathrm{),}$$ in the Schumann–Runge continuum region. No emission of the (1, 1) and (2, 2) atmospheric bands has been observed indicating that under the conditions employed, ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}>\hspace{0.17em}0)}$ is either initially formed only to a relatively small degree in this mechanism or that ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}>\hspace{0.17em}0)}$ is relaxed or quenched by O₂ within less than 10³ collisions. From the (0, 0) band fluorescence decay rates measured at O₂ pressures from 0.02 to about 0.5 torr a quenching rate constant of 4.5 × 10⁻¹⁶ cm³ molecule⁻¹·sec⁻¹ is derived. At higher pressures, the decay rate deviates from a linear dependence on the O₂ pressure indicating that the reactive lifetime is influenced by some secondary process at these pressures. The decay rate measured for example at 20 torr, O₂ would correspond to a quenching coefficient of 4.8×10⁻¹⁷ cm³ molecule⁻¹·sec⁻¹. Quenching of ${\mathrm{O}}_2{\mathrm{(b}}^1{\Sigma }_g^{+}\text{, υ′\hspace{0.17em}=\hspace{0.17em}0)}$ by He, Ne, Ar, Kr, Xe, H₂, N₂, CO, CO₂, SF₆, NH₃, H₂O, CH₄, C₂H₆, C₂H₄, NO, NO₂, and N₂O has been investigated by measuring reactive lifetimes at constant O₂ pressures as a function of the added foreign gas pressures. Quenching rate constants are reported and compared with previous results.