Femtosecond spectroscopy of the (2)1Σ+ u double minimum state of Na2: time domain and frequency spectroscopy

Abstract

Abstract.Femtosecond time resolved pump-probe experiments studying wave packet dynamics in the (2) is,+ double minimum state of Na2 are reported. The experiments were performed in a molecular beam with ion Time of Flight (TOF) detection. By Fast Fourier Transformation (FFT) of the observed time domain data the energy spacings of the coherently coupled vibrational levels in the (2) tZ~ potential are obtained with an accuracy of 0.02 cm-1, although an ultrafast laser source with its inherent spectral width was used in the experiment.The wavelengths of the pump and probe laser pulses are chosen such that in this two color experiment we can control ionisation versus ionisation induced fragmentation.In order to study the influence of the potential barrier on a vibrational wave packet motion we performed simulations based on time dependent quantum calculations.

FEMTOSECOND LASER PHOTOELECTRON SPECTROSCOPY ON ATOMS AND SMALL MOLECULES: Prototype Studies in Quantum Control

“…For ionization at 544 nm negligible ionization was predicted for the inner potential well, whereas an oscillating dipole moment was calculated for the barrier and the outer well (37). In a two-color 340 nm pump and 540 nm probe experiment, ions from the outer turning point were detected to obtain spectroscopic information for the Na 2 doubleminimum state (74). Using kinetic energy time-of-flight mass spectroscopy in a one-color (341.5 nm) pump-probe scheme (75), the dynamics of the wavepacket on the Na 2 double-minimum state was mapped.…”

Pump/probe direct photoionization from thermally hot samples: the Cs2 molecule

“…Zewail and coworkers showed how time-resolved pump/probe signals can be used to determine potential energy curves very accurately for the I 2 molecule [5]. The same analysis has been carried through for the sodium dimer [6]. In the present study we report quantum calculations on the pump/probe ionization spectroscopy of Cs 2 using a model of four electronic states.…”

“…The signals can be evaluated numerically either by discretizing the energy continuum [20,21] or using a basis set expansion [19]. Here we choose an alternative way: a very useful approximation to calculate / υ I E without repeating the time-integration for each energy E is to neglect all kinetic energy operators which appear under the integral in (6). The conditions for the validity of this "short-time-approximation" can be explicitely worked out [22].…”

Accurate Potential Curve for the Double Minimum 21Σ+ State of Na2

“…In fact the experimental energy levels in such case do not necessarily agree with the eigenenergies of the adiabatic potential. (15)(16)(17) because the intrinsic potential barrier influences the wave-packet motion. Gerber and co-workers (16) have already demonstrated for this state a possibility of transforming femtosecond time domain data into precise information about vibrational spacings in frequency domain.…”

“…(15)(16)(17) because the intrinsic potential barrier influences the wave-packet motion. Gerber and co-workers (16) have already demonstrated for this state a possibility of transforming femtosecond time domain data into precise information about vibrational spacings in frequency domain. Therefore we believe that the potential energy curve presented here may be useful not only for testing calculations in the field of quantum chemistry but also for interpretation of femtosecond laser spectroscopy experiments.…”