【Abstract】 The collision-free multiphoton ionization and dissociation of jet cooling methyl nitrite (CH3ONO) were studied by using intense dye laser around 440nm. NO+ ion peak in the TOF mass spectrum was obtained under different accelerating electric field and different angle (χ) between laser polarization plane and the tals of the flight tube.NO+ peak is broadened when NO comes from the dissociation of CH3ONO and this broadening becomes more apparent under lower accelerating electric field. NO+ peak shape is also influenced by the property of laser polarization. ir the accelerating electric field is low enough, there are three peaks when χ=0 and only one peak when χ=90°. These phennomena can be explained by CH3ONO’s two-photon transition from S0 to S2 repulsive state. NO thus produced has a large velocity parallel to the laser polarization plane.更多还原