Water molecules in ultrashort intense laser fields

Abstract

Ionization and excitation of water molecules in intense laser pulses are studied theoretically by solving the three-dimensional time-dependent electronic Schrodinger equation within the single-active-electron approximation. The possibility to image orbital densities by measurement of the orientation-dependent ionization of H2O in few-cycle, 800 nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbital 1b(1) is found to dominate the overall ionization behavior, contributions from the energetically lower lying 3a(1) orbital dominate the ionization yield in the nodal plane of the 1b(1) orbital. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even for laser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelope phase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects have to be considered

Analytical model for calibrating laser intensity in strong-field-ionization experiments

“…If these yields are compared to ionization probabilities calculated using accurate theoretical methods, then intensity calibration in the experiment can be accomplished. Accurate calculations of ionization probability for a fixed laser intensity can be accomplished by solving the timedependent Schrödinger equation (TDSE) for atoms and some small molecules [8][9][10][11][12][13][14][15][16][17][18][19], mostly based on the single-activeelectron (SAE) model. Calculations including all electrons in the atom or molecules have been used within the timedependent density functional theory (TDDFT) [20][21][22][23][24][25], the time-dependent Hartree-Fock (TDHF) theory [26,27], or the multiconfiguration time-dependent Hartree-Fock (MCTDHF) theory [28][29][30].…”

Imaging of the umbrella motion and tunneling in ammonia molecules by strong-field ionization

“…This is the case if for an oriented molecule the direction of the electric field maximum with respect to the dipole moment (see Fig. 4) leads to significantly different ionization yields for the parallel and antiparallel orientations as was demonstrated and discussed for the water molecule [26]. Fig.…”

“…The time-dependent Schrödinger equation (TDSE) describing the electronic response for a fixed nuclear geometry is solved using the single-determinant approach which has been described in detail in our previous works [4,10,25,26]. Briefly, a multi-center B-spline approach is used to solve the Kohn-Sham hamiltonian.…”

Application of the weak-field asymptotic theory to tunneling ionization ofH2O

“…[7], the molecular strong-field approximation (MO-SFA) [8,9] in Ref. [10], and by time-dependent density functional theory (DFT) [11], the time-dependent configuration-interaction singles and singles-doubles approach [12], and within the singleactive-electron approximation (SAEA) to the time-dependent Schrödinger equation [13][14][15][16]. The results of these approaches disagree on which orientation of the molecular principal inertial axis through the O atom that maximizes the ionization yield with respect to the field direction.…”