The Born-Oppenheimer approximation of uncoupled electronic and nuclear motion is a standard tool of the computational chemist. However, its validity for molecule-metal surface reactions, which are important to heterogeneous catalysis, has been questioned because of the possibility of electron-hole pair excitations. We have performed experiments and calculations on the scattering of molecular hydrogen from a catalytically relevant metal surface, obtaining absolute probabilities for changes in the molecule's velocity parallel to the representative Pt(111) surface. The comparison for in-plane and out-of-plane scattering and results for dissociative chemisorption in the same system show that for hydrogen-metal systems, reaction and diffractive scattering can be accurately described using the Born-Oppenheimer approximation.

Two-color (800-and 400-nm) short (45-fs) linearly polarized pulses are used to ionize and dissociate CO and NO. The emission of C q + , N q + , and O + fragments indicates that the higher ionization rate occurs when the peak electric field points from C to O in CO and from N to O in NO. This preferred direction is in agreement with that predicted by Stark-corrected strong-field-approximation calculations.

Abstract:We study the evolution of nuclear wave packets launched in molecular nitrogen, oxygen and carbon monoxide by intense 8fs infrared pulses.We use velocity map imaging to measure the momentum of the ion fragments when these wave packets are interrogated by a second such pulse after a variable time delay. Both quasi-bound and dissociative wave packets are observed. For the former, measurements of bound-state oscillations are used to identify the participating states and in some cases extract properties of the relevant potential energy surfaces. Vibrational structure is resolved in both energy and oscillation-frequency for the cations of oxygen and carbon monoxide, displaying the same quantum wave packet motion in both energy and time domains. In addition, vibrational structure is seen in the dication of carbon 2 monoxide in a situation where the energy resolution by itself is inadequate to resolve the structure.