Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)

We have studied the ultraviolet laser-induced desorption of NO molecules fr om an epitaxial film of NiO(100) on Ni(100) for pulse durations of 550 fs a nd at a photon energy of 3.95 eV. For applied laser intensities up to 450 M W/cm(2), the highest intensities employed in this work, a linear dependence of the desorption yield on the laser intensity is observed. A desorption c ross section of (1.9+/-0.3).10(-17) cm(2) is then derived. The molecules ar e detected with rovibrational state selectivity by (1+1)-REMPI via the A (2 )Sigma(+)(v'=0,1,2,3)<--X (2)Pi(v "(')=0,1,2,3) gamma-band transitions. The rotational population distributions are nonthermal, with rotational temper atures of about 290 K at low and of about 770 K at high rotational energies . The relative populations in the (2)Pi(1/2) and (2)Pi(3/2) fine-structure states and of the Lambda-doublet states are examined for the given set of ( v ",J ") quantum numbers. The vibrational states v "> 0 are significantly p opulated approaching vibrational temperatures of 3800 K. Velocity distribut ions of the desorbed molecules are measured for individual rovibrational st ates. Bimodal distributions with a distinct rotational-translational coupli ng are observed. Further, molecules desorbing in the excited fine-structure state (2)Pi(3/2) show a higher velocity than those desorbing in (2)Pi(1/2) . The results are compared with earlier ones obtained for the same system w ith nanosecond desorption pulses at h nu=6.4 eV. (C) 1999 American Institut e of Physics. [S0021-9606(99)70225-4].