Search

Dissociation of acetaldehyde in moderate strong laser field of 10[sup 13]–10[sup 14] W/cm[sup 2] was investigated. Singly charged parent ion CH[sub 3]CHO[sup +] and fragmental ions CH[sub 3][sup +], CHO[sup +], C[sub 2]H[sub 4][sup +], O[sup +], CH[sub 2]CHO[sup +], and H[sup +] were produced by 800 nm laser of 100 fs pulse duration and recorded by time-of-flight mass spectrometer. The CH[sub 3][sup +] fragment further dissociated to CH[sub 2][sup +], CH[sup +], and C[sup +] ions at higher intensity. Ab initio calculated results show that the singly-, doubly-, and triply charged parent ions are stable. So, the dissociation mechanism was not due to Coulomb explosion of multicharged ion. A field-assisted dissociation (FAD) theory, which assumes that only one bond undergoes dissociation while the rest of the molecular geometry stays unchanged, was employed to treat the dissociation dynamics. Accordingly, the dressed potential energy surfaces of the ground state for the parent and the fragment ions were calculated. Corresponding quasiclassical trajectory calculations show that the bond ruptures take place in the order of C–C, C–O, and C–H, agreeing with the observation. The observed angular dependence and charge distribution of the product ions can also be interpreted by the FAD theory. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports that Methanol was irradiated by 80 fs laser pulse, intensity range of 10&sup13;–10&sup14; W/cm² and that a TOF-mass spectrometer was coupled to the laser system and used to detect the ions produced. Statement that the parent ions CH&sub3;OH&sup+; appeared firstly at the laser intensity of 1.4 × 10&sup13; W/cm²; Discussion of how the laser intensity was gradually increased while the parent ions were dissociated and the primary ions CH&sub2;OH&sup+; were given as verified from the irradiation of deuterated methanol (CH&sub3;OD) showing the C—H bond cracking firstly; Increase of the laser intensity to 2.0 × 10&sup13; W/cm² while the C O bonds of the parent ions also broke to give CH&sub3;, &sup+;; Statement that when the laser intensity was higher, smaller fragment ions like CH&sup+;, C&sup+;, OH&sup+; and O&sup+; also appeared; Evidence that among the fragment ions, only H&sup+; ion yield had anisotropic angular distribution dependence on the laser polarization vector in the dissociation of methanol; Demonstration that all the experimental observations show that the dissociation of methanol proceeds through stepwise mechanism but not Coulomb explosion.