A new method for studying carbon clusters in the gas phase: Observation of size specific neutral fragment loss from metastable reactions of mass selected C+<i>n</i>, <i>n</i>≤60

Abstract

A new method for studying the generation and structure of carbon cluster ions is described. A rotating, translating carbon rod is subjected to the focused output of an excimer laser operating at 308 nm. The resulting plume is directly sampled by a high resolution reverse geometry mass spectrometer operating between 2 and 8 kV. In this paper we report initial results for the positive cluster ions up to n=60. The mass spectra are bimodal with a minimum occurring between C+26 and C+31 in agreement with findings of other workers using related techniques. Metastable neutral loss is observed for all cluster ions with n≥5. Below C+30 the most intense neutral loss is C3 but intense C1 and C5 loss is observed for a significant number of systems and C10 and C14 for a few systems. Above C+30 the metastable loss spectra dramatically change and only C2, and a minor amount of C4 loss, is observed. The C+60 ion is slightly enhanced in the mass spectrum but its metastable reactivity is no different than any of the other C+n ions above n=30. The detailed results are interpreted in terms of stable structures of both the parent ions and neutral fragments that have been predicted theoretically.