State-to-State Surface Scattering of Methane

We report first results for state-to-state surface scattering experiments for CH$_{\mathrm{4}}$. A molecular beam of CH$_{\mathrm{4}}$, incident on a single crystal Ni(111) surface, is prepared in a single rovibrationally excited quantum state by infrared pumping using a continuous wave optical parametric oscillator. State prepared CH$_{\mathrm{4}}(\nu _{\mathrm{3}}$, J$=$2) collides with the Ni surface with controlled incident energy and angle and the scattered CH$_{\mathrm{4}}$ molecules are detected with quantum state resolution using a cryogenic bolometer in combination with infrared laser tagging. Using this setup, we measured rotational and vibrational state distributions for methane scattered from bare Ni(111), graphene covered Ni(111), and LiF(100)$_{\mathrm{.}}$ The results provide detailed information on the rotational and vibrational energy transfer between the incident CH$_{\mathrm{4}}(\nu _{\mathrm{3}}$, J$=$2) molecules and the target surface. Efficient vibrational energy transfer is observed for incident CH$_{\mathrm{4}}(\nu _{\mathrm{3}})$ leading to scattered CH$_{\mathrm{4}}(\nu _{\mathrm{1}})$ where $\nu_{\mathrm{3}}$ and $\nu_{\mathrm{1}}$ are the anti-symmetric and symmetric C-H stretch normal modes of CH$_{\mathrm{4}}$, respectively. Energy transfer probabilities to other vibrational states of CH$_{\mathrm{4}}$ including the vibrational ground state are currently under investigation and will be reported in this contribution.