共查询到20条相似文献,搜索用时 609 毫秒
1.
N. Amin S. Mahmood M. Saleem M. A. Kalyar M. A. Baig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):331-337
The photoionization cross-sections from the 2p2P1/2, 3/2, 3d2D3/2, 5/2 and 3s2S1/2 excited states of lithium have
been measured at different ionizing laser wavelengths, above the first
ionization threshold. The experiments are performed by using a thermionic
diode working in the space charge limited mode and the cross-sections are
measured by employing the saturation technique. By changing the ionization
photon energy, a smooth frequency dependence of the cross-sections has been
observed for the 2p and 3d states. The cross-section from the 3s excited
state has been measured at a single photon energy. The measured values of
the photoionization cross are compared with the available data. 相似文献
2.
H. P. Liu Z. G. Sun S. D. Hogan N. Q. Lou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(3):357-362
We report an experimental study of the multiphoton dissociation dynamics of
CF3I performed on a home-built femtosecond laser pump-probe system, with
time-of-flight mass spectrometer. The first repulsive A band and the
5pπ37sσ υ2=1 Rydberg state of CF3I were accessed
by one- and two-photon transitions at 267 nm, respectively, with the latter
two-photon absorption followed by a further two-photon probe transition at
401 nm to the
state of the parent ion. The observed signals
from the CF3
+ and I+ fragments show similar multi-component
exponential decay patterns but the former is 4 times stronger than the
latter. However, the parent CF3I+ signal was observed to evolve in a
very different manner, decreasing sharply when probed in the first 289 fs
following excitation and subsequently rising again after 860 fs to a
constant level below that measured at negative pump-probe delay times when the
pump and probe pulses exchange roles. This dip observed in the parent ion
profile, is very different from that previously reported at shorter pump
wavelengths of 264 nm or 265 nm, and is interpreted as the competition
between two different ionization channels. One from the vibrationally excited
υ2=1 of the irradiated Rydberg state and the other from the
dissociative vibrational origin of the same electronic state which is
populated by internal vibrational relaxation. 相似文献
3.
M. A. Baig S. Mahmood M. A. Kalyar M. Rafiq N. Amin S. U. Haq 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):9-16
We report new measurements of the oscillator strengths of the 3p
2P3/2 ↦nd 2D5/2, 3/2 and 3p 2P1/2 ↦
nd 2D3/2 Rydberg transitions of sodium using a thermionic diode ion
detector in conjunction with the Nd:YAG pumped dye lasers. The ns
2S1/2 and nd 2D5/2,3/2 Rydberg series have been recorded
via two-step excitation, from the 3p 2P3/2 and 3p 2P1/2
intermediate states. Employing the saturation technique, the photoionization
cross sections from the 3p 2P3/2 and 3p 2P1/2 intermediate states at the first ionization threshold are determined as 7.9(1.3) Mb and 6.7(1.1) Mb respectively. The f-values
of the Rydberg transitions are calibrated with the photoionization cross section measured at the first ionization threshold
and compared with the earlier data. 相似文献
4.
T. Halfmann K. Böhmer L.P. Yatsenko A. Horsmans K. Bergmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):113-123
We report the observation of pronounced coherent population trapping and dark resonances in Rydberg states of xenon. A weak
two-photon coupling with radiation of = 250 nm is induced between the 5p6
1
S
0 ground state of xenon and state 5p
56p[1/2]0, leading to (2+1) resonantly enhanced three-photon ionization. The state 5p
56p[1/2]0 is strongly coupled by radiation with ≃ 600 nm to 5p
5
ns[J
C]1 or 5p
5
nd[J
C]1 Rydberg states with principal quantum numbers n in the range 18 ?n? 23 and with the rotational quantum number of the ionic core J
C = 1/2 or J
C = 3/2. The ionization is monitored through observation of the photoelectrons with an energy resolution ΔE = 150 meV which is sufficient to distinguish the ionization processes into the two ionization continua. Pronounced and robust
dark resonances are observed in the ionization rate whenever is tuned to resonance with one of the ns- or nd-Rydberg states. The dark resonances are due to efficient population trapping in the atomic ground state 5p6
1
S
0 through the suppression of excitation of the intermediate state 5p
56p[1/2]0. The resolution is sufficient to resolve the hyperfine structure of the ns-Rydberg levels for odd xenon isotopes. The hyperfine splitting does not vary significantly with n in the given range. Results from model calculations taking the natural isotope abundance into account are in good agreement
with the observed spectral structures. Pronounced dark resonances are also observed when the dressing radiation field with
is generated from a laser with poor coherence properties. The maximum reduction of the ionization signal clearly exceeds
50%, a value which is expected to be the maximum, when the dip is caused by saturation of the transition rate between the
intermediate and the Rydberg state due to incoherent radiation. This work demonstrates the potential of dark resonance spectroscopy
of high lying electronic states of rare gas atoms.
Received 7 May 2000 and Received in final form 25 June 2001 相似文献
5.
V. M. Apatin V. N. Lokhman D. D. Ogurok D. G. Poydashev E. A. Ryabov 《Journal of Experimental and Theoretical Physics》2011,112(1):1-9
The results of the investigation of the multiphoton ionization of (CF3I)
n
clusters by ultraviolet laser radiation are reported. The yields of the I2+ and I+ ions, which are the products of the multiphoton ionization, have been measured as functions of the intensity of the ultraviolet
radiation at the wavelengths of 308 and 232.5 nm. The degree of multiphoton ionization has been determined and appears to
depend on the wavelength of radiation. The velocity distributions of the products have been measured in detail for various
wavelengths and various polarizations of radiation. The anisotropy parameters of the velocity distributions of the produced
ions and their kinetic energy have been determined. After analysis of the data, a mechanism of the multiphoton ultraviolet
ionization of the clusters under investigation has been proposed. This mechanism depends on the used wavelengths. 相似文献
6.
V. M. Apatin V. O. Kompanets V. N. Lokhman N. -D. D. Ogurok D. G. Poydashev E. A. Ryabov S. V. Chekalin 《Journal of Experimental and Theoretical Physics》2012,115(4):567-578
The excitation and ionization of CF3I molecules and their clusters by femtosecond UV laser pulses is studied. It is concluded that the types of excitation of free CF3I molecules and their clusters by femtosecond UV laser pulses are different. The composition and kinetic energy of ion products observed upon the ionization of (CF3I) n clusters by femtosecond pulses are found to differ considerably from those obtained upon ionization by nanosecond pulses. It is shown that the molecular I 2 + ion is produced in reactions induced in (CF3I) n clusters by UV radiation. Using the pump-probe method, we found the two channels of producing I 2 + ions with characteristic times ??1 ?? 1 ps and ??2 ?? 7 ps. A model of the reactions under study proposed in the paper is consistent with our experimental results. 相似文献
7.
M.A. Baig M. Yaseen Raheel Ali Ali Nadeem S.A. Bhatti 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,6(2):201-209
We report new measurements on laser-assisted molecular dissociative sequential excitation and ionization spectra of strontium
vapor. A single Nd:YAG pumped dye laser in conjunction with an atomic beam apparatus have been used to investigate the even
parity 5snd
3,1
D
2
Rydberg series resulting from the 5s5p
1
P
1
resonance level. The relative intensities changes among the 5snd
3
D
2
and 1
D
2
Rydberg series are attributed to the interactions with the 4d6s
1,3
D
2
perturbers, respectively. The interchannel interactions between the 5snd
1
D
2
series and the 4d6s
1
D
2
level and among the 5snd
3
D
1,2,3
series and the 4d6s
3
D
1,2,3
intruders have been separately parameterized using the two-channel quantum defect theory.
Received: 10 September 1998 / Received in final form: 16 December 1998 相似文献
8.
S. Ring B. Schmidt H. Baumgärtel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,3(2):155-158
We have studied the ionization of Rydberg-excited xenon atoms in THz-laser fields and by quantum dynamical calculations. The
experimental threshold laser field strength for 10% ionization probability follows an n*-1.68 (1.04 THz) dependence (n* effective principal quantum number) with additional weak resonance structures and shows that ionization does not occur by
a Landau-Zener mechanism. At scaled frequencies of to 5.6 the simulated threshold fields for ionization in oscillatory fields show a dependence on the principal quantum number
n of n-4.1 to n-1.35.
Received: 17 February 1998 / Revised: 20 April 1998 / Accepted: 21 April 1998 相似文献
9.
P. Müller B.A. Bushaw W. Nörtershäuser K. Wendt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,12(1):33-44
Isotope shifts and hyperfine structure have been measured in 4snp 1 P1 and Rydberg states for all stable calcium isotopes and the radioisotope 41Ca using high-resolution laser spectroscopy. Triple-resonance excitation via
Rydberg state was followed by photoionization with a CO2 laser and mass selective ion detection. Isotope shifts for the even-mass isotopes have been analyzed to derive specific mass
shift and field shift factors. The apparent isotope shifts for 41Ca and 43Ca exhibit anomalous values that are n-dependent. This is interpreted in terms of hyperfine-induced fine-structure mixing, which becomes very pronounced when singlet-triplet
fine-structure splitting is comparable to the hyperfine interaction energy. Measurements of fine-structure splittings for
the predominant isotope 40Ca have been used as input parameters for theoretical calculation of the perturbed hyperfine structure. Results obtained by
diagonalizing the second-order hyperfine interaction matrices agree very well with experimentally observed spectra. These
measurements allow the evaluation of highly selective and sensitive methods for the detection of the rare 41Ca isotope.
Received 17 December 1999 and Received in final form 29 March 2000 相似文献
10.
I. C.H. Liu J. M. Rost 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):65-71
We investigate properties of ultralong-range polyatomic
molecules formed with a Rb Rydberg atom and several ground-state atoms whose
distance from the Rydberg atom is of the order of n2a0, where n is the
principle quantum number of the Rydberg electron. In particular, we put
emphasis on the splitting of the energy levels, and elucidate the nature of
the splitting via the construction of symmetry-adapted orbitals. 相似文献
11.
V. N. Lokhman D. D. Ogurok E. A. Ryabov 《Journal of Experimental and Theoretical Physics》2006,103(1):1-14
The results of experimental studies of multiphoton ionization of CF2HCl molecules and clusters by UV laser radiation in the wavelength range 217–236 nm are reported. In the case of molecules, the main reaction products are CF2H+ and CF+ ions as well as atomic chlorine. It is found that the spectra of the products of ionization of free molecules and molecules condensed into clusters differ qualitatively: multiphoton ionization of clusters does not yield CF2H+ ions. The dependences of the ion yield on the intensity of laser radiation and its wavelength are measured. The effect of a constant electric field and the radiation spectral width on the multiphoton ionization process is demonstrated. The shape of the velocity distributions is determined for a number of products. A strong anisotropy is detected in the reaction of formation of CF2H+ ions. Possible mechanisms for these processes are discussed. 相似文献
12.
L.A.A. Nikolopoulos Takashi Nakajima P. Lambropoulos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):297-304
Calculations of intense field (around 1016 W/cm2) single- and double-ionization processes in helium at XUV wavelengths are presented. The laser wavelength is chosen near
the | 2s2p
1
P autoionization structure and the dynamics are explored. Single and double ionization yields, as well as the photoelectron
energy spectrum for photon energies around the autoionization structure are calculated. In the case of a pulse of few femtoseconds
duration, no significant enhancement of the double ionization yield has been found in tuning the photon frequency around the
peak of the resonance. It is also shown that in the case of a long pulse (and hence narrow compared with the relevant autoionization
width), the branching ratio of double to single ionization yield can be relatively enhanced by tuning to the absorption minimum
of the resonance.
Received 19 February 2002 / Received in final form 2 May 2002 Published online 19 July 2002 相似文献
13.
S. Westermann T. Amthor A. L. de Oliveira J. Deiglmayr M. Reetz-Lamour M. Weidemüller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):37-43
We investigate excitation transfer and migration
processes in a cold gas of rubidium Rydberg atoms.
Density-dependent measurements of the resonant population exchange
for atoms initially excited into the 32P3/2(|mJ|=3/2) state
are compared with a Monte Carlo model for coherent energy
transfer. The model is based on simulations of small atom
subensembles involving up to ten atoms interacting via coherent
pair processes. The role of interatomic mechanical forces due to the
resonant dipole-dipole interaction is investigated.
Good agreement is found between the experimental data and the
predictions of the model, from which we infer that atomic motion
has negligible influence on the energy transfer up to Rydberg
densities of 108 cm-3, that the system has to be described in terms
of many-body dynamics, and that the energy transfer
preserves coherence on microsecond timescales. 相似文献
14.
M.N.R. Ashfold S.R. Langford R.A. Morgan A.J. Orr-Ewing C.M. Western C.R. Scheper C.A. de Lange 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(2):189-197
Resonance enhanced multiphoton ionization (REMPI) spectroscopy, preferably linked with kinetic energy analysis of the resulting
photoelectrons (REMPI-photoelectron spectroscopy (PES)), continues to make enormous contributions to our understanding of
the spectroscopy and, in many cases, the decay dynamics of small molecules in excited (normally Rydberg) electronic states.
Here we present results of recent REMPI and REMPI-PES studies involving the ammonia molecule which provide further illustration
of some of the many opportunities offered by these techniques.
Received: 28 January 1998 / Revised: 3 April 1998 / Accepted: 15 April 1998 相似文献
15.
T. L. Andreeva S. V. Kuznetsova A. I. Maslov I. I. Sobel'man 《Journal of Russian Laser Research》1983,4(1):65-84
A method of investigating reactions of excited and unexcited atoms is discussed. It is based on pulsed photolysis of molecules with simultaneous passage of laser radiation through the working medium. The method proposed is used to investigate the reactions that accompany the photolysis of the molecules RI(CF3I, n-C3F7I, i-C3F7I). The rate constants of the recombination of iodine atoms into I2 in the presence of RI molecules are calculated for the atoms I(2P3/2) and I*(2P1/2), as are the recombination constants of the radicals R into R2 and with the atoms I*(2P1/2) and I(2P3/2) into the RI molecule. It is shown that the I(2P3/2) atoms are much more active in the recombination into Ia and RI than the I*(2P1/2) atoms. The role of the investigated reactions in the kinetics of a photodissociation iodine laser (PDIL) is discussed. The results are compared with the published data. 相似文献
16.
X. H. Ren J. T. Zhang Y. Wang Z. Z. Xu D. S. Guo 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(3):401-407
We study the photoelectron angular distributions (PADs) of diatomic molecule
H2
+ irradiated by intense laser fields using a nonperturbative
scattering theory. We find that the internuclear vector may change the PADs.
The PADs have qualitative changes with the increasing of the internuclear
distance. The molecular orientation affect the symmetry of the PADs. When the
internuclear vector is vertical or parallel to the laser polarization vector,
the PADs are four-fold symmetric; for other case the PADs are two-fold
symmetric. Due to the modulation effect resulting from the molecular
multi-core nature, the size of the jet and the main lobe can be enlarged or
reduced. The molecular modulation effect become obvious for large
internuclear distance. 相似文献
17.
T. L. Andreeva S. V. Kuznetsova A. I. Maslov I. I. Sobel'man E. A. Yukov 《Journal of Russian Laser Research》1983,4(1):91-97
A method for separating iodine isotopes is proposed, based on the large difference between the rate constants of the excited I*(2P1/2) and unaxclted iodine atoms with radicals CF3 and with Cl2 molecules, and on the possibility of selectively acting on the127I atoms in the states2P1/2 and2P3/2 by radiation from a photodissociation R127I iodine laser (λ = 1.315 μm). The possibility of separating the pure isotope129I and the mixture127I with129I is investigated. 相似文献
18.
V. N. Lokhman D. D. Ogurok E. A. Ryabov 《Journal of Experimental and Theoretical Physics》2009,108(5):727-737
The results of investigation of dissociation of (CF3I) n clusters upon resonant excitation of vibrations of CF3I molecules by pulsed CO2 laser radiation are reported. The kinetics of dissociation of such clusters is studied and the dissociation yield is measured. It is shown that its value is completely controlled by fluence ΦIR of transmitted IR radiation energy and its time dependence is exponential. The results of measurements show that the dissociation lifetime of clusters is shorter than 10?8 s. The velocity and translational temperature of free CF3I molecules formed during dissociation of clusters are measured, as well as the dependence of these parameters on ΦIR. It is concluded that, under these conditions of IR excitations, the dissociation of (CF3I) n clusters can be treated as consecutive evaporation of molecules. 相似文献
19.
M. Fifirig A. Cionga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):33-39
We study the “coherent phase control” between the three-photon ionization by a fundamental laser field and the one-photon
ionization by its third harmonic for a hydrogen atom in its ground state. The relative phase δ of the harmonic field with
respect to the fundamental laser radiation “modulates” the interference between the two ionization channels, which is important
near the crossing points between the ionization rates of the two individual processes. Numerical results for the total ionization
rate and for the angular distribution of the photoelectrons as a function of the phase δ are presented for frequencies located
in the vicinity of the atomic resonances corresponding to the absorption of two laser photons.
Received 31 August 2000 and Received in final form 6 February 2001 相似文献
20.
A. Nadeem M. Nawaz S. U. Haq S. Shahzada M. A. Baig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(2):147-151
We report term energies and quantum defects of highly excited even-parity states of mercury in the 83 876–84 140 cm-1 energy range, employing a two-step laser excitation scheme via the S0↦6s6p3P1 inter-combination transition. Two dye lasers, pumped by a common Nd:YAG laser, were frequency doubled by BBO crystals and
used to record the spectra in conjunction with a thermionic diode ion detector. Our new observations include the much extended
D2 (22 ≤n ≤52) series and a few members of the S1 (24 ≤n ≤30) Rydberg series. Members of the D2 Rydberg series with such a high n value are reported for the first time. The relative intensities of the D2 and S1 transitions (m = 4, 5 and 6) of group II-B elements excited from the P1 inter-combination states are also discussed. 相似文献