Isotope effects in the gas phase radiolysis of H₂S and D₂S

Abstract

. Can. J. Chem. 54, 2767Chem. 54, (1976. Gas phase radiolysis studies have been carried out on mixtures of H2S and D2S using as irradiation sources, either a Gammacell or a Febetron 705 pulsed electron accelerator. Separation factors (CY = (H/D)prOd i (H/D)react) were obtained for various values of xD (the mole fraction of D2S), dose rate and temperature, as well as with the addition of SFs. All of the observed CY values, for 0.2 5 xD 5 0.8, fall on the following empirical straight line.[I] CY(X,) = (1.18 f 0.04) + (1.07 + 0 . 0 9 )~~ The addition of neon to a D2S/H2S mixture gives a value of CY which decreases as the partial pressure of neon increases. For a 70% D2S/305L H2S mixture, = 1.9 + 0.1 for the pure mixture and 1.28 + 0.08 when 90 kPa of neon has been added to 10 kPa of the mixture. The a values described by eq. 1 are interpreted as arising from kinetic isotope effects in the reactions of (translationally) hot H or D atoms with H2S, HDS, or D2S to form HZ, HD or D2.Hydrogen yields from the gas phase radiolysis of pure H2S and pure D2S have been determined for dose rates from 4 X 1016 to 2 x 1028eV g-1 s-1. Using dose rates of up to 2 X 1027eV g-1 s-1, AG = G(H,) -G(D2) = 0.5. For the highest dose rate used (2 X eV g-I S-I), AG = 1.5. The larger value of AG at very high dose rates is thought to arise from the dissociative neutralization processes. A possible mechanism is discussed. [I] a(xD) = (1.18 + 0.04) + (1.07 + 0 . 0 9 )~~ L'addition de neon i un melange de D2S/H2S donne une valeur CY qui diminue comrne la pression partielle dp nCon augmente. Pour un melange D2S/H2S, 70:30, CY = 1.9 + 0.1 pour le mClange pur ef 1.28 0.08 quand 90 kPa de nCon a Ct C ajoutC B 10 kPa du mClange. Les valeurs CY dkrites par 1' Cq. 1 sont interpretkes comme venant des effets cinetiques dans les rhctions d'atomes H ou D, riches en Cnergie de translation, avec HIS, HDS ou D2S pour former HZ. HD ou DL. Les rendements en hydrogkne de la radiolyse en phase gazeuse de H2S pur et D2S pur ont kt6 dCterminCs pour des taux d'irradiation de 4 X 1016 eV g-I s-1 B 2 X lozs eV g-1 s-1. Utilisant des taux d'irradiation jusqu'i 2 X lO27eV g-1 s-1, AG = G(H2) -G(D2) = 0.5. Pour le plus grand taux d'irradiation utilise (2 X 10z8 eV g-1 s-I), AG = 1.5.On croit que la plus grande valeur de AG B des taux d'irradiation trks eleves est attribuable aux processus dissociatifs de neutralisation. Un mkanisme possible est discute.[Traduit par le journal]