화학공학소재연구정보센터
Journal of Chemical Physics, Vol.111, No.1, 386-397, 1999
Femtosecond ultraviolet laser-induced desorption of NO from NiO(100)/Ni(100)
We have studied the ultraviolet laser-induced desorption of NO molecules from an epitaxial film of NiO(100) on Ni(100) for pulse durations of 550 fs and at a photon energy of 3.95 eV. For applied laser intensities up to 450 MW/cm(2), the highest intensities employed in this work, a linear dependence of the desorption yield on the laser intensity is observed. A desorption cross section of (1.9+/-0.3).10(-17) cm(2) is then derived. The molecules are 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 temperatures 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 populated approaching vibrational temperatures of 3800 K. Velocity distributions of the desorbed molecules are measured for individual rovibrational states. Bimodal distributions with a distinct rotational-translational coupling 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 with nanosecond desorption pulses at h nu=6.4 eV.