| Time-resolved Fourier transform spectroscopy (TR-FTIRS) has been developed based on standard digital signal processing (DSP) technology and a modified commercial continuous scan Fourier transform infrared spectrometer (FTIRS). Preliminary tests show that changes as low as 0.02 monolayers to CO/Pt(111) can be detected. The system can achieve a maximum time resolution of 500 ns and spectral resolution of 0.75 cm-1. The technique is flexible; it can be implemented on a variety of DSP and hardware platforms; maximum time resolution is limited in principle only by the A to D conversion rate, whereas spectral resolution is determined by the commercially available spectrometer. The data acquisition (DAQ) system has been proven operational using a mock transient CO vibrational signal from a slow scanning spectrometer (52.7 Hz), simulated by an amplitude modulated (carrier) sine wave.; TR-FTIRS has been implemented for the first time in the field of surface science, to study the effects of laser induced thermal perturbation (LITP) of CO/Pt(111). Inhomogeneities in the beam result in usable power densities of less than or equal to 25 MW/cm2, resulting in at most partial desorption. In all cases, including lower than required power densities for any desorption, the chemical system is perturbed from equilibrium, and re-equilibration is slower than expected. We tentatively conclude that the CO*/Pt precursor → CO/Pt chemisorbate pathway is microscopically reversible such that sub-desorption power densities cause CO adsorbates to temporary occupy precursor states above the surface.; Future TR-FTIRS experiments will benefit from the signal to noise improvements from gain ranging via a home-built programmable gain amplifier (PGA). Tests show that S/N is improved by at least a factor of three by selectively amplifying the low intensity (high digital noise) regions of the interferograms generated by the TR-DAQ system. |
