Exploring surface photoreaction dynamics using pixel imaging mass spectrometry (PImMS)

Abstract

A new technique for studying surface photochemistry has been developed using an ion imaging time-of-flight mass spectrometer in conjunction with a fast camera capable of multimass imaging. This technique, called pixel imaging mass spectrometry (PImMS), has been applied to the study of butanone photooxidation on TiO2(110). In agreement with previous studies of this system, it was observed that the main photooxidation pathway for butanone involves ejection of an ethyl radical into vacuum which, as confirmed by our imaging experiment, undergoes fragmentation after ionization in the mass spectrometer. This proof-of-principle experiment illustrates the usefulness and applicability of PImMS technology to problems of interest within the surface science community.

Translational and Rotational Energy Distributions of NO Photodesorbed from Au(100)

“…This seems to be in agreement with the angular distributions, where a thermal desorption mechanism seems to be responsible for the slower NO molecules after 266 nm photodesorption, as indicated by the fitting parameter n ≤ 1. In our previous work we have shown that NO desorption was induced predominantly by a nonthermal desorption mechanism at 355 nm . We note that the temperature rise during laser irradiation is only ∼27 K for 355 nm pulses, i.e., transient surface temperatures are ∼205 K, but we also showed that NO still adsorbs to our substrate at those temperatures.…”

“…In our previous work we have shown that NO desorption was induced predominantly by a nonthermal desorption mechanism at 355 nm. 26 We note that the temperature rise during laser irradiation is only ∼27 K for 355 nm pulses, i.e., transient surface temperatures are ∼205 K, but we also showed that NO still adsorbs to our substrate at those temperatures. The temperature jump for 266 nm irradiation is ∼20 K (due to slightly lower laser fluences), and while the photon energy is higher than at 355 nm, the shorter wavelength photons seem to preferentially induce a thermal process.…”

“…Recently, a number of groups began to exploit the advantages of the velocity map imaging (VMI) techniqueso far predominantly used for gas-phase studiesfor surface dynamics studies. − We previously reported on the use of a combination of time-of-flight (TOF) and VMI techniques for resolving 3-dimensional velocity distributions of NO photodesorbed from a gold single crystal using 355 nm photons . NO molecules were found to leave the surface preferentially along the surface normal with a very narrow angular and rather fast velocity distribution, indicating a nonthermal desorption process.…”

Ion and velocity map imaging for surface dynamics and kinetics

“…Others have previously reported using position sensitive detection methods for studying surface scattering, 30 based on ion imaging [31][32][33] or velocity map imaging techniques, which were developed at around the same time as those for the gasphase imaging experiments. 34,35 These have predominantly used a geometry in which the surface and the detector are parallel, [36][37][38][39][40][41] which is convenient for the production of the imaging electric fields but prevents the projection of the full velocity distribution in the scattering plane onto the detector. Our new imaging setup (shown in Fig.…”

Fast sensors for time-of-flight imaging applications

“…The PImMS sensor has also been employed as a detector in time-resolved velocity-map imaging studies into gas-phase 16 and surface 17 photochemistry. Configured as an optical sensor, the camera is mounted outside the vacuum in place of the CCD camera in a conventional VMI detection setup.…”