The radical cation of formaldehyde in a freon matrix. An electron spin resonance study

Abstract

Exposure of highly purified very dilute rigid solutions of formaldehyde in CFCl₃ at 77 K to ⁶⁰Co γ-rays gave e.s.r. spectra assignable to H₂CO^˙+ radical cations. The parameters obtained were similar to those previously assigned to H₂CO^˙+ cations in rare-gas matrices, there being no superhyperfine coupling to chlorine, in marked contrast with results for acetaldehyde cations, whose e.s.r. spectra showed a characteristic anisotropic quartet splitting from one chlorine nucleus. The method of generating formaldehyde was critical: when very low concentrations of impurities such as 1,3,5-trioxane were present, cations therefrom were formed preferentially, and no clear features for H₂CO^˙+ were resolved. E.s.r. features characteristic of Me₂O^˙+ cations were obtained in some cases; possible reactions leading to this impurity are discussed. New e.s.r. data for 1,3,5-trioxane radical cations are presented, obtained at ca. 30 K, which show the presence of two strongly coupled protons (A= 142 G), and two sets of two weakly coupled protons (A₁= 13 G, A₂= 25 G).