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1.
Th. Freudenberg W. Radloff H. -H. Ritze V. Stert K. Weyers F. Noack I. V. Hertel 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1996,36(3-4):349-364
The formation of protonated and unprotonated ammonia cluster ions is studied by femtosecond two colour two photon pump-probe techniques applied to (NH3) n and (ND3) n clusters withn up to 8. The fourth harmonic (~ 200 nm, 6.2 eV, 160 fs) of a Ti: Sapphire laser pulse is used to excite the clusters in a state corresponding to theà state of NH3 while the third harmonic (267 nm, 4.65 eV) is used for the subsequent ionisation step. Employing a combination of the optical Bloch equations for the excitation process and rate equations for the cluster dynamics we calibrate the zero time delay and carefully analyse the time dependence of the pump-probe signal. Several distinct intermediate steps in the time evolution can be distinguished, having characteristic time constants ranging from 40 fs to over 100 ps. They are discussed in a consistent scheme for the excitation, ionisation and protonation dynamics, accounting also for characteristic differences observed between deuterated and undeuterated species. A particularly remarkable time dependence of the homogeneous (NH3) 2 + cluster ion signal is interpreted as a fingerprint of internally protonated neutral precursors of the type NH3NH2NH4. 相似文献
2.
Steinkellner O Noack F Ritze HH Radloff W Hertel IV 《The Journal of chemical physics》2004,121(4):1765-1770
Two-photon excitation with femtosecond laser pulses in the spectral range 240-250 nm was used to prepare vapor phase H(2)O and D(2)O in the C (1)B(1) and D (1)A(1) states. Both states are predissociated via the B (1)A(1) state, forming excited OH/OD(A (2)Sigma(+)) as well as ground state OH/OD(X (2)Pi). We used ultrashort infrared probe pulses (1.65-2.42 microm) to control the ratio between these excited and ground state fragments originating from the dissociation process. Time resolved detection of the OH/OD(A (2)Sigma(+)) --> OH/OD(X (2)Pi) fluorescence allows us to monitor the dynamics of the predissociation. For the heterogeneous predissociation out of the C(1)B(1) state life times of (0.5 +/- 0.1) ps and (1.2 +/- 0.1) ps were found for H(2)O and D(2)O, respectively. The purely homogeneous character of the predissociation out of the D (1)A(1) state was monitored. 相似文献
3.
The optically induced polarization change was studied in the case of a standing elliptically polarized wave. Using a Zeeman-tuned
gas laser at 3.39 μm with an internal methane cell we have demonstrated the influence of the dichroism on the nonlinear absorption
signals. 相似文献
4.
By means of nonlinear absorption spectroscopy data necessary for the interpretation of molecular spectra can be obtained in
such spectral regions, where conventional spectroscopic methods yield only a quasi-continuous absorption curve. Using a Zeeman-tuned
He−Ne laser at the wavelength of 3.39μm we have measured significant differences in the intensity and temperature behaviour
for several ethane absorption lines, the analysis of which made possible a preliminary qualitative assignment of these lines. 相似文献
5.
6.
P. Farmanara H.-H. Ritze V. Stert W. Radloff I.V. Hertel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):193-209
Neutral ammonia clusters (NH3)m are photo-excited to the electronic state by a deep UV femtosecond laser pump pulse. Within a few hundred femtoseconds a significant fraction of the clusters
rearrange to form an H-transfer state (NH3)m-2NH4(3s)NH2 with the subunit NH4 in its 3s electronic ground state. This state is then electronically excited by a time-delayed infrared control pulse of variable wavelength.
Finally, a third (probe) pulse in the UV ionizes the clusters for detection. The lifetime of the excited (NH3)m-2NH4(3p)NH2 states is found to vary between 2.7 and 0.13 ps depending on cluster size and excitation energy. It increases drastically
upon deuteration. The corresponding cluster size-dependent photoelectron spectra allow us to disentangle the underlying energetics
of the excitation and ionization process and reveal additional processes, such as nonresonant ionization or dissociative ionization.
The experimental findings suggest that the excited H-transfer ammonia complexes with m > 2 are deactivated by an internal conversion process back to the electronically lowest H-transfer state followed by fast
dissociation.
Received 22 September 2001 and Received in final form 31 January 2002 相似文献
7.
K. Weyers Th. Freudenberg H. -H. Ritze W. Radloff V. Stert 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,39(3):217-223
Applying the 2CR2PI method we have obtained novel information about the spectral structures of the heterodimers C6H6 · NH3 and C6H6 · ND3 near the S1 state of benzene. For the first time the ionization threshold and the dissociation energy of the heterodimers have been determined. Preliminary results of ab initio calculations reveal that one of the two suggested isomers is characterized by hydrogen-bonded configurations with hindered rotation of ammonia about its C 3 axis. The calculated dissociation energy D 0 of this isomer very well agrees with the value of (620±100) cm-1 determined experimentally. Exciting the heteroclusters to energy levels near the S 2 state of benzene no 2CR2PI signals were obtained due to fast internal conversion. 相似文献
8.
3 cm-l for a wavelength of λR≈200 Å in a time ≲1 ps can be expected. The measurable gain Greal depends on the cluster density Ncl. For Ncl≈1016 cm-3 we expect Greal≳20 cm-1.
Received: 30 October 1997 相似文献
9.
H. -H. Ritze 《Zeitschrift für Physik B Condensed Matter》1980,39(4):353-360
The influence of the self-induced optical anisotropy appearing in the wings of a degenerate dipole transition on the quantum properties of elliptically or linearly polarized monochromatic light is calculated in the Heisenberg picture. Further the photon statistics (bunching or antibunching) of the weak field detected after passing a phase retarder and a polarizer is studied. Finally the possibility to measure small deviations from the Poisson distribution without coincidence experiments is discussed. 相似文献
10.
As a model to correlate light modes we consider the nondegenerate three-wave interaction in parametric approximation. The correlated modes are made to interface with each other and the photon statistics of the resulting field is investigated. A possible enhancement of photon antibunching is clearly shown and discussed. 相似文献