Field ionization of aliphatic ketones by intense femtosecond laser

Field ionization of acetone, butanone, and 3-pentanone in an intense laser field is experimentally investigated by using a femtosecond laser and a time-of-flight mass spectrometer. Theoretically, the ionization process is treated by using a molecular orbital-based model. The nonbonding P-x electron in the oxygen atom is considered as the most feasibly ionized electron and the x axis as the most feasibly ionized vector. The electrostatic potential is obtained by combining the ab initio potential of the molecule and the external potential. The tunneling probability of the P-x electron through the potential barrier is numerically calculated by the transfer matrix method. The ionization probability is modified by the spatial and temporal corrections for a pulsed laser beam, and the total ion yields can thus be obtained. The calculated laser power dependence of the ion yield agrees well with the experimental data measured in the range of 3.5 x 10(13)-1.2 x 10(14) W/cm(2).