Above Threshold Dissociation Of Monovalent CO Molecules

In the last few decades,with the laser pulses continues to develop in a super-intense and ultra-short direction,the ionization and dissociation dynamics of the diatomic molecules have been widely studied.Some intriguing and important experimental phenomena have been observed,such as enhanced ionization?EI?,bond softening?BS?,bond hardening?BH?and above-threshold dissociation?ATD?.The molecules are dissociated after ionization using strong laser field,the time-of-flight mass spectra of the fragment ions are measured,and the ionization dissociation information of molecules in the laser field are obtained,such as kinetic energy release?KER?of different dissociation channels.Further,these information provides important experimental data,which can help people control the molecular dissociation and chemical reactions by femtosecond laser pulses.In this work,a femtosecond laser with a central wavelength of 800 nm and a pulse duration of 30 fs are employed,using the time-of-flight mass spectrometer?TOF-MS?technique.We systematically investigate the above-threshold dissociation of CO⁺molecules by measuring the relationship between TOF mass spectra of the C⁺ions,at different laser intensities and fixed polarization angle.The angle between the laser polarization direction and the TOF axis is 18o,and the laser intensity varies from3.5�10¹⁴ W/cm² to 1.35�10¹⁵ W/cm².Different TOF mass spectra of C⁺ions are obtained as function of laser intensity.The structure of the spectrum does not change apparently in the given intensity range,which indicates that the production mechanism of C⁺ions remains the same.Furthermore,the TOF mass spectra C⁺ions are measured by fixing the laser intensity as 1.35�10¹⁵ W/cm² and changing the angle between the laser polarization direction and TOF axis.The experimental data shows that the C_center?1,0?signal grows stronger and stronger with the increase in the angle between the laser polarization and TOF axis,and extents to its maximum at 90^o.However,the C_split?1,0?signal on both sides of the central peak becomes weaker and weaker,and shrinks to its minimum at 90^o.For better understating of the relation between the laser polarization direction and the TOF mas spectra of C⁺,and the work established the dissociation picture of the CO⁺molecular ions.We believe that the monovalent CO molecular ions,which are produced by the interaction of CO molecules with laser,are mainly populated the lowest three molecular ion states,i.e.X²?⁺,A²?,and B²?⁺,and then the CO⁺molecular ions in the A²?and B²?⁺state are reached a dissociation state through a multiphoton process,and the molecular ions dissociate.Here,it is found that the three possible dissociation pathways,which are parallel?|B²?⁺-0?>?|3²?⁺-3?>?,perpendicular?|A²?-0?>?|1²?^--3?>,|B²?⁺-0?>?|D²?-2?>?transitions.The measu--red C⁺ions in this work are obtained from the dissociation of the above three different states.Based on this physical description,the TOF mass spectra of C⁺ions is simulated under different laser polarization conditions,the simulation results are consistent with the experimental results,indicating the rationality of our physical picture.