The Ionization And Dissociation Mechanism Of Cyclohexanone Within Intense Femtosecond Laser Field

The study of molecules in intense ( I?1 01 4 W/cm2) laser with super-short (Ï„?10?13s) pulse duration has developed very fast over last two decades. Because of the complicated structure characteristic of organic molecules and its important position in the nature, the study of organic molecules photolysis process with super-intense laser has got a homologous progress.The experiment that we analyze in this paper is that the organic molecule cyclohexanone decomposes induced within intense laser field. In our experiment, one laser pulse is Split into two laser pulses, their wavelength is 800nm, and their pulse duration is 90fs. The delay time between two bunches of laser is changed by changing the length of optical path of the weak laser. The molecule beam of cyclohexanone is produced by jetting molecules into the vacuum cavity by pulse valve. In our experiment, we can understand the dissociation processes of molecule cyclohexanone by analyzing the mass spectrum.In this paper, we simulate the laser intensity changing with time at first. We assume that the waveform of laser intensity is Gauss waveform. In the simulation pictures, we find out that the laser intensity vibrates strongly whenthe delay time approaches zero. We think that, the phenomenon is caused by the two laser pulses interfering with each other. When the delay time is zero, the peak value of the laser intensity is more than three times stronger than one bunch of laser.We think that there are two characteristic processes of multiphoton absorbing repeatedly in the process of multiphoton absorbing dissociation: (one) two processes of multiphoton absorbing are consecutive; (two) two processes of multiphoton absorbing are not consecutive, there is a process of decaying between the two multiphoton absorbing processes. There are four kinds of main dissociation channels exiting in the dissociation process of molecule cyclohexanone in intense laser field: (1) the characteristic of multiphoton absorbing dissociation channel is similar to process (one), the life of the middle production is long, The dissociation channel is named D1 dissociation channel; (2) the characteristic of multiphoton absorbing dissociation channel is similar to process (one), the life of the middle production is short, the dissociation channel is named D2 dissociation channel; (3) the characteristic of multiphoton absorbing dissociation channel is similar to process (two), the life of the middle production is long, The dissociation channel is named D3 dissociation channel;(4) the characteristic of multiphoton absorbing dissociation channel is similar to process (two), the life of the middle production is short, The dissociation channel is named D4 dissociation channel. Analyzing the experiment data, we can find out that, when the later intensity is weak, the D1 dissociation channel is the main channel, when the laser intensity becomes stronger, the D4 dissociation channel is the main channel, when the later intensity is strongest, the D3 dissociation channel is themain channel. There are two or more channels exiting with the changing of the laser intensity.By analyzing the mass spectrum, we think there are two kinds of ions. The dissociation channel of C2H2+,C2H3+ and C3H3+ ions is similar. The dissociation channel of C2HO+,C2H2O+ and C3H3O+ ions is similar too. Contrasting the ion intensity of six kinds of fragment ions, the probability of the positive charge centre on the oxygen atom moving to the carbon atom of carbonyl is smaller than the probability of the positive charge centre moving to the carbon atom near the carbonyl. The positive charge centre is important to promote the dissociation processes of the matrix ion. The moving of H atom is important to promote the dissociation processes too.