Dissociation mechanism of electronically excited CHn (n = 3–5) neutrals formed by near-resonant neutralization using charge inversion mass spectrometry
Department of Chemistry, Graduate School of Science, Osaka Prefecture University, 1-1 Gakuen-cho, Sakai, Osaka, 599-8531, Japan
Corresponding author: a email@example.com
Revised: 31 October 2005
Published online: 17 January 2006
Charge inversion mass spectrometry was used to produce the electronically excited species CHn (n=3–5) from their corresponding positive ions by neutralization with an alkali metal target, and then to subsequently detect and mass-analyze the negative ions formed from the neutral fragments produced from the dissociation of the excited neutrals. The trapezoidal shape and the intensity of the peak associated with CH2- ions in the charge inversion spectrum of CH3+ ions indicated that the CH3 neutrals dissociated mainly into CH2 + H without a large activation barrier. The most intense peak in the spectrum of CH4+ ions was that associated with CH2- ions, and this peak comprised a combination of both trapezoidal and triangular shaped peaks. The trapezoidal shaped peak was attributed to CH2- ions resulting from direct dissociation of CH4 into CH2 + H2. The concurrent dissociation of CH4 into CH3 + H was followed by the further subsequent dissociation of the deformed CH3 fragments into CH2 + H, and this was proposed to be the origin of the triangular shaped component of the CH2- peak. In the spectrum of CH5+ ions, the CH3- peak was much less intense than the CH2- peak, which was proposed to be the result of the geometry of the CH3, formed from the dissociation of CH5 into CH3 + H2, being substantially distorted from the D3h symmetry, leading to its further subsequent dissociation.
PACS: 34.50.Gb – Electronic excitation and ionization of molecules; intermediate molecular states (including lifetimes, state mixing, etc.) / 34.70.+e – Charge transfer / 34.50.Lf – Chemical reactions, energy disposal, and angular distribution, as studied by atomic and molecular beams
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2006