Coincidental emission of molecular ions from keV carbon cluster impacts

Abstract

We report here experimental data for the emission of one and two phenylalanine (Ph) molecular ions per impact from 10 to 21 keV impacts of coronene (C 24H 12), C 60, and gramicidin S (C 60N 12O 10H 92) projectiles as a function of projectile mass, energy, and geometry. Secondary ion mass spectrometry (SIMS) experiments were conducted using event-by-event bombardment and detection. With this method, individual projectile impacts and the resulting secondary ions are recognized as singular events resolved in time and space. The target surface was an equa-molar mixture of phenylalanine (Ph H, C 9H 11NO 2) and deuterated phenylalanine (Ph D, C 9H 3D 8NO 2). This allowed for the detection of two co-emitted [M-H] − phenylalanine ions in a dual time-of-flight instrument. In contrast to the linear dependence yield of Ph versus energy for single Ph ion emission, the yield for two Ph ion emission versus energy is nonlinear within the experimental energy range. For the co-emission of two Ph ions, C 60 was found to be more efficient than coronene at equal velocities.