The dynamic Auger–Doppler effect in HF and DF: control of fragment velocities in femtosecond dissociation through photon energy detuning (original) (raw)
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Analysis of the resonant Auger decay during ultrafast fragmentation of CH3F
AIP Conference Proceedings, 2006
After inner shell excitation the ultrafast fragmentation of small molecules can proceed on a time scale similar to that of the Auger decay. In this case the nuclear motion affects the observed electron spectrum in various ways. The best known example is the Doppler splitting of atomiclike Auger lines, but non-parallel potential surfaces are equally important. Using an electron energyion momentum coincidence experiment and an ab initio calculation of potential curves, we discuss the main features seen in the non-coincident and coincident resonant Auger spectrum by decay of the F(1s) → 6a * core excited state of CH 3 F.
Dissociation of the CF 1 4 molecular ion has been investigated using monochromatized synchrotron radiation and the energy-selected electron-ion coincidence method. The 2t 21 2 C ionic state produces fragment ions CF 1 2 and CF 1 3 . The branching ratio CF 1 2 ͞CF 1 3 is increased by a factor of ϳ6 by the C 1s excitation to the lowest unoccupied antibonding orbital, from the ratio at the direct ionization of the 2t 21 2 orbital. This increase is interpreted in the light of the nuclear motion in the core-excited state, with the help of theoretical calculations based on the vibronic model. PACS numbers: 33.80.Gj, 33.15.Mt, 33.20.Rm, 33.80.Eh Recent developments of the synchrotron radiation light sources and related beam line techniques allow one to excite any core electron to a specific quantum state using a narrow-band soft x-ray beam and to investigate the relaxation dynamics of the core-excited state in detail. Extensive observations of the resonant Auger processes and their theoretical analyses have revealed that the significant nuclear motion can take place within the lifetime of the core-excited states in some diatomic molecules . Extensive observations of the ionic fragmentation of core-excited polyatomic molecules, on the other hand, revealed that the change of the molecular structure can take place in the core-excited states . These findings enforce us to give up the conventional idea that the molecular dissociation starts at the Auger final state where the Auger transition is terminated and motivate us to examine the effect of the nuclear motion in the core-excited state on the molecular dissociation, i.e., the nuclear motion in the Auger final state.
The dynamical behaviour of H2 and D2 in a strong, femtosecond laser field
Detailed measurements of H 2 and D 2 dissociation fragment kinetic energy dependences on laser intensity, using 150 fs, 800 nm pulses, are presented. The yields for both molecular and atomic ions are also given. The observed three-peak kinetic energy spectrum carries within it the signature of the different stages of the interaction. The two lower energy peaks are a product of bond softening (and above threshold) dissociation of the molecular ion from Franck-Condon populated vibrational levels. The third higher-energy peak results from enhanced ionization of the dissociating molecular ions. No light-induced vibrational trapping need be invoked to interpret the higher-energy fragments.
Ultrafast dissociation: An unexpected tool for probing molecular dynamics
Journal of Electron Spectroscopy and Related Phenomena, 2012
Ultrafast dissociation following core-shell excitation into an antibonding orbital led to the early observation in HBr of atomic Auger lines associated to the decay of dissociated excited atoms. The purpose of this article is to review the very large variety of systems where such a situation has been encountered, extending from simple diatomic molecules toward more complex systems like polyatomics, clusters, or adsorbed molecules. Interestingly, this phenomenon has revealed an extremely rich and powerful tool for probing nuclear dynamics and its subtle interplay with electron relaxation occurring on a comparable time scale. Consequently this review covers a surprisingly large period, starting in 1986 and still ongoing.
Control of molecular breakup by an infrared pulse and a femtosecond pulse train
Physical Review A
We investigate the dissociation dynamics of diatomic molecules subjected to both a femtosecond infrared (IR) laser pulse and a femtosecond pulse train (FPT) within the framework of the Morse potential model. When the IR and FPT are phase delayed, we observe well-resolved oscillations in dissociation probability, corresponding to multiple integers of the IR period, exhibiting enhancement and suppression of bond dissociation. These oscillations reveal a rich dynamics as a function of the IR and FPT parameters including chaotic fields. A frequency-resolved profile of dressed molecular states shows that these oscillations are due to interference of many quantum paths analogous to the recently observed control of photoionization of atoms under IR and XUV pulses. By manipulating phases of FPTs we demonstrate an enhancement of molecular dissociation compared to the transform-limited case.
Femtosecond dissociation of ozone studied by the Auger Doppler effect
The Journal of Chemical Physics, 2001
A Doppler-type shift in the kinetic energy of atomic Auger electrons emitted after fast dissociation of O 3 molecules is observed. The resonant Auger spectrum from the decay of repulsive core-excited states reflects both the early molecular ozone decay and that from excited dissociation fragments. The kinetic energy of the fragment is manifested as an energy shift of the atomic Auger lines when the measurement is made under certain conditions. We report measurements of the energy-split atomic fragment emission lines arising from dissociation on a time scale comparable to the core-hole lifetime. For the O 1s -* states the kinetic energy release amounts to several electron volts. We report measurements for excitation of both the terminal and central oxygen 1s electrons. A simple kinematic model for extracting a lower limit for the kinetic-energy release is presented and is compared with the result of a Born-Haber cycle, which may be seen as an estimate of the maximum energy release.
Dynamics of Light-Field Control of Molecular Dissociation at the Few-Cycle Limit
Physical Review Letters, 2007
We studied the laser-molecule interaction dynamics that leads to the asymmetric D ion ejection in the dissociative ionization of D 2 molecules observed recently in Kling et al. [Science 312, 246 (2006)]. By changing the carrier-envelope phase, we showed that the asymmetry is a consequence of manipulating the initial ionization and the rescattering of the electrons within one optical cycle of the laser. The result illustrates the feasibility of coherent control of reaction dynamics at the attosecond time scale.
Observing Femtosecond Fragmentation Using Ultrafast X-ray-Induced Auger Spectra
Applied Sciences
Molecules often fragment after photoionization in the gas phase. Usually, this process can only be investigated spectroscopically as long as there exists electron correlation between the photofragments. Important parameters, like their kinetic energy after separation, cannot be investigated. We are reporting on a femtosecond time-resolved Auger electron spectroscopy study concerning the photofragmentation dynamics of thymine. We observe the appearance of clearly distinguishable signatures from thymine s neutral photofragment isocyanic acid. Furthermore, we observe a time-dependent shift of its spectrum, which we can attribute to the influence of the charged fragment on the Auger electron. This allows us to map our time-dependent dataset onto the fragmentation coordinate. The time dependence of the shift supports efficient transformation of the excess energy gained from photoionization into kinetic energy of the fragments. Our method is broadly applicable to the investigation of photofragmentation processes.
Steering a molecule into dissociation via vibrational excitation
New Journal of Physics, 2009
For a laser driven molecule, we show that the ionization and the dissociation channels can be separated by preparing the molecule in a specific vibrational state. Specifically, we investigate the dynamics of the hydrogen molecular ion under a femtosecond infrared laser field aligned with the molecular axis. We find dissociation probabilities of more than 60%, considerably higher than reported so far. We demonstrate that a full dimensional description of the electron dynamics is necessary to obtain accurate results for the combined ionization/dissociation dynamics. Recent intriguing theoretical results have revealed that electron localization during molecular dissociation of the hydrogen molecular ion by pulsed laser excitation can be controlled by using the carrier envelope phase [1], leading to maximal dissociation probabilities slightly above 20%. The competing process of ionization has to be kept at a minimum to achieve this goal experimentally, however [2]. Also, with monochromatic laser light, achieving dissociation is a relatively difficult task [3]. Consequently, high intensity is required for dissociation, for instance, I ≈ 10 15 W cm −2 for a hetero-nuclear diatomic like HF [4]. Even in the case of half cycle pulse fields, which have a very broad frequency content, intensities I > 10 13 W cm −2 are required to achieve on the order of 15% dissociation probability [5]. At such high intensities,