Isomerization processes in ions of the empirical formula C4H8+

journal article
Published by National Institute of Standards and Technology (NIST) in Journal of Research of the National Bureau of Standards Section A: Physics and Chemistry

Vol. 75A (6) , 591-605
https://doi.org/10.6028/jres.075a.048

Abstract

Ions of the formula

C_{4} H_{8}^{+}

have been generated with different initial energies by ionizing ethylene (

C_{2} H_{4}^{+} + C_{2} H_{4} \to C_{4} H_{8}^{+}

, where the

C_{4} H_{8}^{+}

ion is formed with an initial energy of > 11.51 eV), cyclobutane (initial energy of

C_{4} H_{8}^{+}

, > 10.84 eV), methylcyclopropane (> 10.15 eV), 1-C₄H₈ (> 9.58 eV), and i-C₄H₈ (> 9.06 eV) with 11.6-11.8 eV photons, and in some cases also with 10 eV photons and with gamma radiation. The structures of the ions have been determined from the structures of the C₄H₈ products formed in charge transfer reaction between the ions and charge acceptors such as dimethylamine and nitric oxide, as well as from the structures of the butanes formed in

D_{2}^{-}

transfer reactions with methylcyclopentane-d ₁₂ (

C_{4} H_{8}^{+} + C_{6} D_{12} \to C_{4} H_{8} D_{2} + C_{6} D_{10}^{+}

). At low pressures the

C_{4} H_{8}^{+}

ions initially formed in ethylene, cyclobutane, and methylcyclopropane isomerize to the thermodynamically most stable configurations,

{i-C}_{4} H_{8}^{+}

and

{2-C}_{4} H_{8}^{+}

. The

{2-C}_{4} H_{8}^{+}

structure predominates in all the experiments. As the pressure is raised, the

{i-C}_{4} H_{8}^{+}

ion yield diminishes as that of

{2-C}_{4} H_{8}^{+}

increases, indicating that when the precursor of the

{i-C}_{4} H_{8}^{+}

ion is collisionally deactivated, it ends up as

{2-C}_{4} H_{8}^{+}

. At high pressures,

{1-C}_{4} H_{8}^{+}

ions are intercepted; their yield increases with increasing pressure, indicating that

{1-C}_{4} H_{8}^{+}

is an intermediate which isomerizes further unless it is collisionally deactivated. The

{1-C}_{4} H_{8}^{+}

ion formed in methylcyclopropane (initial energy > 10.15 eV) is more easily deactivated than that formed in cyclobutane (initial energy > 10.84 eV). That the isomerization of the

{1-C}_{4} H_{8}^{+}

ion to lower energy structures such as

{i-C}_{4} H_{8}^{+}

and

{2-C}_{4} H_{8}^{+}

requires excess internal energy is demonstrated by the fact that in the photolysis with 10 eV photons, a negligible amount of isomerization is observed, but with 11.6-11.8 eV photons, more than half of the

{1-C}_{...}

Keywords

This publication has 0 references indexed in Scilit: