The dissociation dynamics of diatomic molecules in intense laser fields

Abstract

We have used interferometric techniques to show unambiguously that the fragment ion energies produced in the multielectron dissociative ionization (MEDI) of iodine vary with laser pulse rise time. A field ionization, Coulomb explosion model is found to reproduce MEDI data on I 2 remarkably well. The lack of features associated with post-dissociative ionization in the MEDI spectra of Cl 2 is explained in terms of low dissociation rates for the singly (and possibly doubly) charged parent ions. These results remove the need for the much discussed, but highly speculative, process of 'laser-induced stabilization'.

Theoretical Investigations of the Electronic and Nuclear Dynamics of Molecules in Intense Laser Fields: Quantum Mechanical Wave Packet Approaches

“…In an intense field, cations created are successively ionized at large internuclear distances (due to enhanced ionization), and the resultant multiply-charged cations undergo Coulomb explosions (due to repulsion among positively charged atomic sites). [9][10][11][12][13][14]24 On the basis of distribution patterns in a covariance map of fragment ions, 109 Cornaggia studied the geometrical structures of CO 2 cations that are about to Coulomb-explode and suggested the existence of a large amplitude bending motion. 110 The structures of created cations can now be precisely determined by measuring the momentum vector distributions with mass-resolved momentum imaging 111 and coincidence momentum imaging.…”

“…Compared to atoms in intense fields, molecules exhibit complex phenomena arising from their additional (vibrational and rotational) degrees of freedom, such as charge-symmetric and -asymmetric dissociation, [7][8][9] alignment with an external field, 10 creation of electronically excited fragments, 11,12 and ionization rates that depend on the internuclear distance. 9,13,14 In intense laser fields (I > 10 13 W cm À2 ), the Coulombic potentials in which the electrons are placed are greatly distorted: [15][16][17][18] A large part of the electron density is transferred among nuclei within a half optical cycle (%1:3 fs for ! ¼ 800 nm light).…”

“…One characteristic of ionization of a molecule in an intense laser field is enhanced ionization; ionization is greatly enhanced at a critical internuclear distance, R c , which is much longer than the equilibrium internuclear distance, R e (known as enhanced ionization). 9,13,14,[27][28][29][30] Enhanced ionization has been experimentally observed for various molecules, 27-30 such as CO 2 23 and benzene molecules. 31 The correlation between ionization and structural deformation plays a key role in fragmentation or reaction processes.…”

First Direct Observation of Coulomb Explosion during the Formation of Exotic Atoms

“…In molecules, the emission of binding electrons is ultimately accompanied by an energetic fragmentation of the atoms, a phenomenon referred to as Coulomb explosion. The fragmentation is usually achieved by intense laser fields [1,2], heavy-ion bombardment [3,4], stripping in thin foils [5], or soft x rays [6].…”

“…In laser-induced Coulomb explosion, fragmentation at distances up to 5 Å has been observed [1,2]. However, to reach that distance, it takes the two ions about 7 fs, which is longer than the time needed to deplete the electronic L shell in both atoms even if the pion or muon is already attached to one of the fragments.…”