Infrared fluorescence from a monolayer of CO on NaCl(100)

Infrared fluorescence has been observed from a monolayer of ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}_{}^{16}{}_{}{}^{}$O on NaCl(100) following vibrational excitation of its fundamental absorption band with a pulsed CO gas laser. Direct time-domain measurements of the fluorescence reveal a lifetime of 4.3 ms. Since fluorescence occurs in the overtone region from high vibrational states, these results demonstrate that energy can be stored in the adsorbate long enough to allow vibrational up-pumping between neighboring molecules. It is suggested that the primary channel for CO vibrational relaxation is Δv=-1 transfer to phonons of the NaCl substrate.