Journal of Physical Chemistry A, Vol.115, No.25, 7356-7361, 2011
XUV Free-Electron Laser Desorption of NO from Graphite (0001)
We report results of femtosecond laser induced desorption of NO from highly oriented pyrolytic graphite using XUV photon energies of hv = 38 eV and h nu = 57 eV. Femtosecond pulses with a pulse energy of up to 40 mu J and about 30 fs duration generated at FLASH are applied. The desorbed molecules are detected with rovibrational state selectivity by (1 + 1) REMPI in the A(2)Sigma(+) - X(2)Pi gamma-bands around gamma = 226 nm. A nonlinear desorption yield of neutral NO is observed with an exponent of m = 1.4 +/- 0.2. At a fluence of about 4 mJ/cm(2) a desorption cross section of sigma(1) = (1.1 +/- 0.4) x 10(-17) cm(2) is observed, accompanied with a lower one of sigma(2) = (2.6 +/- 0.3) x 10(-19) cm(2) observable at higher total fluence. A nonthermal rovibrational population distribution is observed with an average rotational energy of < E(rot)> = 38.6 meV (311 cm(-1)), a vibrational energy of < E(vib)> = 136 meV (1097 cm(-1)) and an electronic energy of < E(cl)> = 3.9 meV (31 cm(-1)),