Radiative lifetimes of excited W I levels

Time-resolved laser-induced fluorescence spectroscopy has been used to measure the lifetimes of 47 selected W I levels with energies between 27800 and 48200 cm^?1. A high-current hollow cathode produces an effusive beam of tungsten atoms and ions in the ground states and in metastable states. Selected states are populated with tunable dye laser pulses. The subsequent fluorescence is measured by means of a Tektronix 1 GHz transient digitizer. By taking into account the separately measured response function of the system the lifetimes can be determined from the full decay curve. All measurements are performed with linearly polarized laser beams adjusted to the magic angle in order to exclude systematic error sources. The decay curves also have been inspected for quantum beats and for saturation effects. A comparison with the scarce literature data is given.     

On the determination of radiative lifetimes of excited Mn I and Mn II levels

Time-resolved laser-induced fluorescence spectroscopy has been used to measure the lifetimes of 46 Mn I and 7 Mn II levels. A high-current hollow cathode produces an effusive beam of manganese atoms and ions in the ground states and in metastable states. Selected states are populated with tunable dye laser pulses. The following fluorescence is measured by means of a Tektronix 1 GHz transient digitizer. Including the separately measured response function of the system in the evaluation procedure the full decay curve can be applied for a determination of the lifetimes. All measurements are performed with linearly polarized laser beams adjusted to the magic angle in order to exclude systematic error sources. A comparison with literature data is given.     

Radiative lifetimes for the B1piu state of the Na2 molecule

A study of the radiative lifetimes calculation of the Na2 B1piu state is presented. RKR electronic potentials are considered. The studied vibrational levels are for v' = 0-33 (B1piu) and v" = 0-65 (chi1sigmag+). The rotation is considered for values of J' = 1-225 (B1piu). The Einstein emission coefficients are calculated for the specified B1piu rovibrational levels (for Q line and R, P lines, for all ground state vibrational levels). With the inverse of Einstein emission coefficients sum, the radiative lifetimes are calculated. These calculated lifetimes are in good agreement with the experimental and previously calculated (with RKR potentials) lifetimes, but now great extension of considered rovibrational levels is considered. The bound-free contribution is irrelevant for Na2 lifetimes of the B1piu state. The perturbation between Na2 B1piu and alpha1sigmau+ states is considered.     

Computed lifetimes of metastable states of the NO2+ dication

Based on the ab initio potential energy, spin-orbit coupling, electronic transition dipole moment, and radial nonadiabatic coupling functions, the energy level positions, lifetimes, and radiative transition probabilities (Einstein A coefficients) have been determined for the lowest electronic states of NO2+ using the log-amplitude-phase, stabilization, and complex-scaling methods. The calculated characteristics are in reasonable agreement to the available experimental data, thus, evidencing the reliability of the theoretical predictions for the characteristics unobserved to date. With the exception of the v相似文献   

Rydberg electron transfer to C6H5NO2: lifetimes and characteristics of the product C6H5NO2- ions

The nature of electron binding in C6H5NO2- ions produced by Rydberg electron transfer in K(np)C6H5NO2 collisions is investigated through measurements of the number and the lifetimes of the product ions and their dependence on Rydberg atom velocity and principal quantum number n in the range 12 相似文献   

Pressure saturation of SO2(3B1 0,0,0) lifetimes

Lifetime data have been obtained for the decay of SO₂(³B₁ 0,0,0) at 25°C over the pressure range of 1–762 torr. The ³B₁ state was populated by direct absorption to eliminate any possible complications in interpretation due to the participation of excited-singlet manifolds. At pressures greater than about 10 torr, the measured lifetimes are longer than predicted from low-pressure Stern–Volmer parameters. This deviation can be interpreted in terms of Freed's theory on collisionally induced intersystem crossing and provides unequivocal evidence to support earlier speculations that the lengthening of the lifetimes at high pressures is due to saturation in depopulation of the ³B₁ state.     

Radiative lifetimes and depopulation cross-sections of excited rubidium2 S and2 D states

The radiative lifetimes of excited rubidiumn ² S (n=8?13) andn ² D (n=6?11) states have been measured using the time resolved laser induced fluorescence method. The cross-sections for depopulation of the excited states in collisions with the ground-state Rb atoms have been determined. The influence of the blackbody radiation on the measured values is discussed.     

Fluorescence lifetimes of formaldehyde (H2CO) in the A1A2 --> X1A2 band system at elevated temperatures and pressures

Fluorescence lifetimes of formaldehyde excited by picosecond laser radiation with a wavelength of 355 nm were determined in nitrogen gas in a cell using time-resolved laser-induced fluorescence spectroscopy. The measurements were conducted at temperatures between 295 and 770 K and pressures up to 10 bar (1 MPa). Detection was broadband in most cases. Temperature and pressure were found to have a quenching effect on the fluorescence. At 295 K and pressures between 1 and 5 bar, decay rates between 0.03 and 0.04 ns(-1) were observed. At 770 K, the decay rates increased from 0.11 to 0.17 ns(-1) as the pressure was raised from 1 to 10 bar. The dependence on pressure was not linear at 1 bar. At 10 bar the linearity is unclear. The dependence on temperature appeared to be exponential.     

Molecular electric properties in electronic excited states: multipole moments and polarizabilities of H2O in the lowest1 B 1 and3 B 1 excited states

Summary The dipole and quadrupole moments and the dipole polarizability tensor components are calculated for the¹ B ₁ and³ B ₁ excited states of the water molecule by using the complete active space (CAS) SCF method and an extended basis set of atomic natural orbitals. The dipole moment in the lowest¹ B ₁ (0.640 a.u.) and³ B ₁ (0.416 a.u.) states is found to be antiparallel to that in the ground electronic state of H₂O. The shape of the quadrupole moment ellipsoid is significantly modified by the electronic excitation to both states investigated in this paper. All components of the excited state dipole polarizability tensor increase by about an order of magnitude compared to their values in the ground electronic state. The present results are used to discuss some aspects of intermolecular interactions involving molecules in their excited electronic states.     

The vibrational structure of the X 1A1 - A 1B1 and A 1B1 - B 1A1 band systems of GeH2/GeD2 based on global potential energy surfaces

Transition probabilities were evaluated for the X (1)A(1)-A (1)B(1) and A (1)B(1)-B (1)A(1) systems of GeH(2) and GeD(2) to analyze the X-->A-->B photoexcitation. Franck-Condon factors (FCFs) and Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the X (1)A(1), A (1)B(1), and B (1)A(1) electronic states and the transition dipole moments for the X-A and A-B systems. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least squares method combined with the Shepard [Proceedings of the 1968 23rd ACM National Conference (ACM, New York, 1968)] interpolation. The barriers to linearity correcting the spin-orbit interaction are evaluated to be 22,000 cm(-1) for the X state, 6300 cm(-1) for the A state, and 560 cm(-1) for the B state. The obtained FCFs for the X-A and A-B systems indicate that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies within the three states. The photoexcitation and fluorescence spectra calculated for the X-A system agree well with the observed spectra. The theoretical lifetimes for lower vibrational levels of the A and B states were calculated from the fluorescence decay rates for the A-X, B-A, and B-X emissions, and the lifetimes for the A state are in good agreement with the observed values except those affected by predissociation.     

电子激发态SO2(A^1A2, B^1B1)分子的碰撞猝灭动力学研究

用四倍频YAG激光(266nm)把SO2分子从电子基态X^1A1激励到电子激发态A^1A2和B^1B1的高振动耦合区, 通过检测自发辐射SO2(B^1B1→X^1A1)的时间分辨信号, 测定了室温(290K)下SO2(A^1A2, B^1B1)被He, 氯代甲烷分子和某些烷烃分子猝灭的速率常数。此外, 还从碰撞配合物模型出发, 对SO2(A^1A2, B^1B1)的猝灭机制进行了讨论。     

The 2B1 ← 2A1 system of nitrogen dioxide

The vibrational structure of the ²B₁ ← ²A₁ system of NO₂ has been assigned to a progression in ν′₂. Vibrational analyses for three isotopic species have been made using a hamiltonian which allows explicitly for a large-amplitude bending vibration. The system origin for the normal isotopic species has been assigned an extrapolated value of 14743.5 cm^?1. The bending potential function is expressed as a rapidly converging Taylor series expansion about the linear configuration. There is no evidence that the equilibrium configuration is nonlinear.     

1B2(1Sigma(u)+) excited state decay dynamics in CS2

The authors report time resolved photoelectron spectra of the (1)B(2)((1)Sigma(u) (+)) state of CS(2) at pump wavelengths in the region of 200 nm. In contrast to previous studies, the authors find that the predissociation dynamics is not well described by a single exponential decay. Biexponential modeling of the authors' data reveals a rapid decay pathway (tau<50 fs), in addition to a longer lived channel (tau approximately 350-650 fs) that displays a marked change in apparent lifetime when the polarization of the pump laser is rotated with respect to that of the probe. Since the initially populated (1)B(2)((1)Sigma(u) (+)) state may decay to form either S((1)D) or S((3)P) products (the latter produced via a spin-orbit induced crossing from a singlet to a triplet electronic surface), this lifetime observation may be rationalized in terms of changes in the relative ionization cross section of these singlet and triplet states of CS(2) as a function of laser polarization geometry. The experimentally observed lifetime of the longer lived channel is therefore a superposition of these two pathways, both of which decay on very similar time scales.     

Intrinsic lifetimes of the excited state of DNA and RNA bases

The lifetimes of the excited state of free nucleobases were measured in the gas phase for the first time. They are, respectively, 1.0 and 0.8 ps for the purine bases adenine (shown above) and guanine and 3.2, 2.4, and 6.4 ps for the pyrimidine bases cytosine, uracil, and thymine at 267 nm. The longer lifetimes of the pyrimidine bases may be associated with their higher propensity toward photodegradation, especially in the case of thymine. The ultrashort lifetime of nucleobases conventionally known in solution was found to be an intrinsic molecular property due to extremely facile internal conversion, and therefore the lifetime should be largely independent of the medium at this energy, that is, whether in vacuo, in solution, or in vivo. The evolutionary selection of nucleobases as the durable carriers of genetic information is suggested to be due to their inherent immunity from photochemical reactions.     

The radiative lifetimes of the first excited state of BO and BO2

A pulsed dye laser has been used to study the fluorescence of BO and BO₂ in the gas phase at low pressure. Radiative lifetimes of 87.2 ± 2.6 and 76.3 ± 1.4 ns were obtained for the (000) and (100) levels of BO₂(A ²Π_u) and of 131 ± 15 and 103 ± 6 ns for levels v¹ = 1 and 2 of BO(A ²Π). Unlike BO₂(A ²Π_u), BO(A ²Π) is strongly quenched by the oxygen carrier.     

Studies of lifetimes of rotationally cooled NO2 using time-resolved fluorescence excitation spectra

A taunble, pulsed dye laser with output in the region of 5750 to 6000 Å was used to excite rotationally cooled NO₂ which was produced by expansion in conjunction with argon carrier gas through a supersonic nozzle. The resulting time-resolved fluorescence excitation spectra were used the lifetimes of various vibronic bands of NO₂ (²B₂). The lifetimes measured were in the region of 15 to 40 μs which were shorter than those obtained from cell experiments. For each individual excitation wavelength, only a single exponential decay was observed from very early times through 250 μs.     

An investigation of the1 B 1 excited states of water

The first seven¹ B ₁ excited states of water are investigated within the framework of the single centre method. Energies, wave-functions and electronic densities are found using one basis set of 25 Slater type orbitals and one of 40 orbitals (both with non-integer principal quantum numbers). All singly excited configurations of¹ B ₁ symmetry are taken into account. For each state the orbital parameters (n's and's) are carefully optimized. The energy differences between neighboring excited states are, when the comparison can be made, in good agreement with experiment as is also the major contributing configuration of each state. Particular emphasis is placed on the electronic rearrangement that occurs during excitation and this is explicitly brought out by the contour maps of the electronic density. These maps show satellite-clouds in the excited states.

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Zusammenfasung Die ersten sieben¹B₁-Zustände von Wasser werden mittels der Einzentrenmethode untersucht. Energien, Wellenfunktionen und Elektronendichten werden auf Grund je eines Basissatzes von 25 bzw. 40 Slater-Funktionen mit nicht-ganzzahligen Exponenten bestimmt. Dabei werden alle einfach angeregten¹ B ₁-Konfigurationen mit einbezogen and für jeden Zustand die Orbitalparameter sorgfältig optimalisiert. Die Energiedifferenzen zwischen benachbarten Zuständen sind in den Fällen, in denen der Vergleich mit dem Experiment möglich ist, richtig. Besondere Bedeutung wird den Elektronenumlagerungen beigemessen, die während der Anregung auftreten; sie werden in den Konturen-Bildern, die die Satellitenwolken in den angeregten Zuständen zeigen, wiedergegeben.

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Resumé Les sept premiers états excités¹ B ₁ de l'eau sont étudiés dans le cadre de la méthode à un seul centre. Les énergies, les fonctions d'onde et les densités électroniques sont trouvés successivement dans des bases de 25 et de 40 orbitales de type Slater (dans les deux cas avec des nombres quantiques prin cipaux non entiers). Toutes les configurations monoexcitées de symétrie¹ B ₁ sont prises en compte. Les paramètres orbitaux (n et sont soigneusement optimisés pour chaque état. Lorsque la comparaison avec l'expérience peut être faite on trouve des différences correctes entre les énergies d'état excités voisins, ainsi qu'une bonne identification des configurations essentielles correspondantes. On insiste particulièrement sur le réarrangement électronique qui se produit au cours de l'excitation et qui est explicitement révélé par les cartes d'isodensité. Ces cartes présentent des nuages satellites dans les états excités.

     

Radiative lifetimes for the B1sigma(u)+ and C1pi states of the H2 molecule

With RKR electronic potentials for the B1sigma(u)+, C1pi(u) and X1sigma(u)+ states in conjunction with Huffaker's correction and appropriate asymptotic functions, the unperturbed radiative lifetimes of rovibrational levels of the B1sigma(u)+ and C1pi(u) states of H2 are calculated. Comparison with previous calculations is presented. Better lifetimes for B1sigma(u)+ are obtained in present work.     

Bond and mode selectivity in the reaction of atomic chlorine with vibrationally excited CH2D2

The title reaction is investigated by co-expanding a mixture of Cl2 and CH2D2 into a vacuum chamber and initiating the reaction by photolyzing Cl2 with linearly polarized 355 nm light. Excitation of the first C-H overtone of CH2D2 leads to a preference for hydrogen abstraction over deuterium abstraction by at least a factor of 20, whereas excitation of the first C-D overtone of CH2D2 reverses this preference by at least a factor of 10. Reactions with CH2D2 prepared in a local mode containing two quanta in one C-H oscillator /2000>- or in a local mode containing one quantum each in two C-H oscillators /1100> lead to products with significantly different rotational, vibrational, and angular distributions, although the vibrational energy for each mode is nearly identical. The Cl+CH2D2/2000>- reaction yields methyl radical products primarily in their ground state, whereas the Cl+CH2D2/1100> reaction yields methyl radical products that are C-H stretch excited. The HCl(v=1) rotational distribution from the Cl+CH2D2/2000>- reaction is significantly hotter than the HCl(v=1) rotational distribution from the Cl+CH2D2/1100> reaction, and the HCl(v=1) differential cross-section (DCS) of the Cl+CH2D2/2000>- reaction is more broadly side scattered than the HCl(v=1) DCS of the Cl+CH2D2/1100> reaction. The results can be explained by a simple spectator model and by noting that the /2000>- mode leads to a wider cone of acceptance for the reaction than the /1100> mode. These measurements represent the first example of mode selectivity observed in a differential cross section, and they demonstrate that vibrational excitation can be used to direct the reaction pathway of the Cl+CH2D2 reaction.