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1.
Two-centre model potential calculations have been carried out for the 2Σ +g,u and 2Π g,u states of Li +2, Na +2, K +2, Rb +2 and Cs +2. Comparison with other model potential calculations suggests that reliable potential curves have been obtained. The results indicate the usefulness of calculating diatomic energies by the method proposed. 相似文献
2.
Absorption and fluorescent scattering of nitrogen laser radiation by a low-pressure RF laboratory plasma ( ne = 10 12 cm −3) has been observed for the first negative system of N 2+. A 67±1 ns lifetime of N 2+ (B 2Σ u+) was experimentally measured from the laser-induced fluorescence. In addition, enough collisionally excited N 2 (B 3Π g) was produced to observe laser-induced fluorescence for the second positive system of N 2. The lifetime of N 2 (C 3Π u) was found to be 41±2 ns. The measured lifetimes are in good agreement with published values calculated from theory. 相似文献
3.
The continuous absorption spectrum of molecular bromine has been examined using laser induced photodissociation spectroscopy. In this technique, Br 2 molecules are photolyzed using a flashlamp-pumped dye laser; the atomic products of the dissociation are then monitored by time-resolved resonance absorption spectroscopy in the vacuum ultraviolet. The relative absorptivities for the transitions B 3Π o+u ← X 1Σ +g and 1Π 1u ← X 1Σ +g have been obtained at 18350, 21010 and 22125 cm −1. 相似文献
4.
Single and multiple photon processes are identified in the 193 nm excimer laser photolysis of CS 2. CS(X 1Σ +, υ = 1 to 5, J = 5 to 45) is observed by dye laser induced fluorescence of the A 1Π ↔ ; X 1Σ + transition, following the single photon 193 nm photolysis of CS 2. Multiple photon 193 nm generation of CS fragment emission from 620 to 170 nm is also reported. A partial assignment of the emission spectrum identifies fluorescence from the CS A′ 1Σ + and A 1Π states. 相似文献
5.
The fraction FΣ of excited-state oxygen formed as b 1Σ g+ was determined for a series of triplet-state photosensitizers in CCl 4 solutions. FΣ was determined by monitoring the intensities of (a) O 2(b 1Σ g+) fluorescence at 1926 nm (O 2(b 1Σ g+)→O 2(a 1Δ g) and (b) O 2(a 1 Δ g) phosphorescence at 1270 nm (O 2(a 1Δ g) → O 2(X 3Σ g−)). Oxygen excited states were formed by energy transfer from substituted benzophenones and acetophenones. The data indicate that FΣ depends on several variables including the orbital configuration of the lowest triplet state and the triplet-state energy. The available data indicate that the sensitizer-oxygen charge transfer (CT) state is not likely to influence FΣ strongly by CT-mediated mixing of various sensitizer-oxygen states. 相似文献
6.
Photofragment fluorescence. From OH and OD(A 2∑ +→X 2π), has been observed following two-photon excitation of H 2O and D 2O in the gas phase with a KrF laser (248 nm). The rotational band contour of the OH fluorescence is the same as that observed following single-photon vacuum ultraviolet photolysis of H 2O at 123.6 nm. 相似文献
7.
A mixture of NF 3 and Ar is passed through an rf discharge in a flow-system to produce, among other species, F and NF 2. When H 2, D 2, or CH 4 are added downstream, reactions with F atoms produce vibrationally excited HF or DF together with H, D, or CH 3. The latter free radicals can react with NF 2, probably by an elimination reaction to produce electronically excited NF: NF 2( 2B 1) + H(D, CH 3) → HF *(DF * + NF(a 1Δ). A vibrational-to-electronic energy transfer process between the products of this reaction then produces the next higher state of NF: HF(ν 2) + NF(a 1Δ) → HF(ν−2) + NF(b 1Σ +). A similar transfer process has also been found between the electronically excited a 1Δ states of O 2 and NF: O 2(a 1Δ) + NF(a 1Δ) → O 2(X 3Σ −) + NF(b 1Σ +). The H or D atoms but not the CH 3 radicals are then found to react with either NF(a 1Δ) or NF(X 3Σ −) to produce electronically excited N( 2D) atoms, which in turn react with the NF(a 1Δ) molecules to produce N 2(B 3Π g). The observed nitrogen first positive radiation has been demonstrated to be produced entirely by this reaction mechanism rather than by the N( 4S) recombination that accounts for the Rayleigh afterglow. In addition, the occurrence of the reaction N( 2D) + N 2O → NO(B 2Π r) + N 2 (X 1Σ +g) has been verified. Finally we have observed emission at 3344 Å, which we attribute to the NF(A 3Π), which has not been previously reported. 相似文献
8.
The electronic and geometrical structures of the low-energy states of 1,4,5,8-naphthalenetetracarboxylic dianhydride parent diimide (1) are studied in terms of the complete active space self-consistent field (CASSCF) method employed at different level with respect to the size and the quality of the active space. In the framework of the vibronic model based on the Franck–Condon (FC) effect the absorption and magnetic circular dichroism (MCD) spectra are studied in the excitation region corresponding to two low-energy 1 1A g → 1 1B 2u and 1 1A g → 1 1B 3u electronic transitions in diimides. In that (visible) excitation region the CASSCF computations with the 5π[4n]5π active space (i.e., the naphthalene-like π orbitals enriched by the four lone pair orbitals of the oxygen atoms) were found to reproduce very well the empirical absorption and the MCD spectra measured for the dicyclohexyl- N, N′-substituted diimide (2). At the same CASSCF/5π[4n]5π level, the electronic absorption of diimides in the near UV excitation region were attributed to the 1 1A g → 2 1B 1u, 1 1A g → 2 1B 3u and 1 1A g → 2 1B 2u electronic transitions; the latter two are mostly localized on the “diimide chromophore”. For these transitions the calculated magneto-optical characteristics, such as sign pattern and intensity distribution in the MCD spectrum, were found to be consistent with that experimentally observed for the diimide 2 compound. 相似文献
9.
In this paper the results of detection of higher excited states of p-fluorotoluene in the gas phase are presented. Within a laser scanning range of 547.0–570.0 nm (3+1) RMPI spectra are obtained, and some vibrational structures on the third electronically excited valence state are observed. According to the polarization characteristic of the multiphoton transition the symmetry of the electronic state is determined as A 1+B 1+3pB 2. Correlated to excited states of benzene, the results show that A 1+B 1 corresponds to 1E 1u and 3pB 2 to 3p 1A 2u. It indicates that the double degeneracy of 1E 1u state does not yet degrade in p-fluorotoluene. Moreover, it occasionally degenerates with 3p 1 A 2u. Furthermore, the electron distribution in the phenyl ring maintains the symmetry of the D 6h point group consistently like in benzene. 相似文献
10.
The radiative lifetimes of nine vibrational levels of the C 3( 1Π u) radical were obtained from decay time studies of the C 3( 1Π u → 1Σ +g) fluorescence induced by a tunable dye laser. The lifetimes of the different vibronic levels were found to be constant within the experimental error limits, namely, τ o = (200 ± 10) ns. The collisional deactivation of the C 3( 1Π u) states by helium gives rate constants between 2.5 and 4 in 10 −11 cm 3 molecule −1 s −1 units. 相似文献
11.
A laser pulse-and-probe method has been used to determine the nascent vibrational populations in NO( v=0–4) and O 2( v=6–11) formed in the thermal reaction: O( 3P) + NO 2 → O 2( v) + NO( v). A frequency-tripled Nd: YAG laser is used to photolyse NO 2, diluted tenfold in Ar, and laser-induced fluorescence spectroscopy in the NO A 2Σ +-X 2Π and O 2 B 3Σ −u -X 3Σ −g electronic band system is used both to follow the kinetics of individual vibrational states and to determine the nascent vibrational distributions. The majority of the NO product is formed in v = 0 and the average vibrational yield is ≈ 4.6%. The O 2 populations fall monotonically from v = 6 to 11 in a distribution close to what is expected on prior grounds. Based on a surprisal analysis, the average vibrational energy yield in O 2 is ≈ 26%. The nature of the reaction dynamics is discussed. 相似文献
12.
Measurements of electron stimulated desorption (ESD) yields of O −, at incident electron energies below 20 eV, from 0.15 monolayers (ML) of O 2 physisorbed at 20 K on a variety of molecular solids have been performed. It is observed that for O 2 condensed on 4 ML of H 2O, the O − signal from dissociative electron attachment (DEA) to O 2 is entirely absent. We attribute this to a complete quenching of the dissociative 2Π u, 2Σ +g, and 2Σ +u, resonances of O −2 by the adjacent water molecules. 相似文献
13.
The Ca( 1D 2, 3P J) + CH 3 → CaI(A,B) + CH 3 reactions system has been studied by measuring its chemiluminescence under beam-gas conditions. Absolute values of the state-to-state reaction cross-sections were determined at low collision energy
. In addition, the electronic branching ratio and product energy disposal have been determined for each metastable reaction. The major changed observed in the chemiluminescence when comparing the Ca( 1D 2) reaction versus that of Ca( 3P J) is the total yield associated with the former reaction. To the best of our spectral resolution neither the electronic branching ratio e.g. CaI(A)/CaI(B) nor the internal CaI energy disposal change significantly as the metastable Ca( 1D 2)/Ca( 3P J) ratio is varied. In spite of the fact that the Ca( 3P J) reaction is less exoergic, the CaI product appears with a higher fraction of internal energy than that of Ca( 1D 2) reaction. Thus, the fraction of the total energy appearing in CaI internal energy amounts to 57.5% in the Ca( 3P J) reaction while it is 19.3% only for the Ca( 1D 2) reaction. This difference is discussed in the light of a distinct mechanism associated with the attack of the excited Ca atom into the C---I bond. No significant chemiluminescence yield was found for the energetically open CaCH *3 channels. The product chemiluminescence polarization was also measured as a function of the metastable concentration. A significant degree of polarization was found depending upon the specific electronic excitation. The analysis of the polarization emission associated to the parallel CaI(X 2Σ+ ← B 2Σ+) emission led into a strong polarization of the product rotational angular momentum. The comparison of the product rotational alignment for the kinematically identical Ca(1D2, 3PJ, 1P1) + CH3 → CaI* (B2Σ+) + CH3 reaction system showed that the CaI rotational polarization diminishes in the 3PJ → 1D2 → 1P1 sequence, e.g. as the reaction exothermicity increases. In addition the degree of polarization associated with other emission bands as for example CaI(X 2Σ+ ← A 2Π1/2) indicates the presence of a parallel transition which was been interpreted as mixing of Hund's case (a) and (c) appropriate for this heavy CaI diatom produced with a high rotational excitation. 相似文献
14.
Mg +—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X 2Σ + → 2Π is observed with an origin at 31387 cm −1 (vac) for 24Mg +—Ar. The 24Mg +—Ar spectrum is characterized by a 15 member progression with a frequency (ω′ e) of 272 cm −1. An extrapolation of this progression fixes the excited state dissociation energy ( D′ o) at 5552 cm −1. The corresponding ground-state value ( D″ o) is 1270 cm −1 (3.6 kcal/mol). The 2Π
,
spin—orbit splitting is 76 cm −. 相似文献
15.
The recombination of nitrogen atoms on polycrystalline samples of cobalt and nickel produces metastable electronically excited nitrogen molecules, probably N 2(W 3Δ u), which are collisionally transferred to the N 2(B 3Πg) state. Information about vibrational relaxation of the metastable state by N 2(X 1Σ +g) is inferred from composition dependent changes in the observed first positive emission spectrum [N 29A 3Σ +g)−N 2(B 3Π g] with the aid of multilevel, steady-state, kinetic model. 相似文献
16.
The spectrum of SO (X 3Σ −) has been observed following the flash excitation of sulphur dioxide with radiation above 250 nm. Sulphur monoxide is produced via an excited molecule mechanism involving triplet SO 2. The rate constant for the reaction 3SO 2 + SO 2 was measured as (3.1 ± 1) × 10 8 M −1 sec −1. 相似文献
17.
The radiative lifetimes of the b 1Σ + and a 1Δ states have been evaluated by perturbation expansions including X 3Σ −, a 1Δ, b 1Σ +, 1 3,1Π, 2 3,1Π, 2 3Σ − and 2 1Σ + states. All wavefunctions result from large MRD CI calculations. The b—X transition is dominated by the parallel transition moment; it is found to be much stronger than the a—X transition. The calculated radiative lifetimes of τ( 1Σ +)=18 ms, τ( 1Δ)=2.2 s for NF and τ( 1Σ +)=2.5–3.5 ms for NCl are in good accord with corresponding experimentally deduced values. The lifetime for the a 1Δ state in NCl is found to be τ( 1Δ)=1.1 s, ie. much longer than derived from a recent experiment. Its magnitude is consistent with the τ(b 1Σ +)/τ(a 1Δ) ratio of similar systems and with the decrease in lifetime from NF to NCl and is thus believed to be quite reliable. A detailed analysis of all contributions of the perturber states to the transition mechanism is made and comparison with the related data in SO, O 2 and S 2 is undertaken. The b-a transition probability dominated by the quadrupole transition is fairly constant in all the systems in the order of A = 0.013 (NF) - 0.0013 (S 2) s −1. 相似文献
18.
Large-basis-set calculations of near Hartree-Fock accuracy were performed on CO +(1σ-hole 2Σ +) and CO +)2σ-hole, 2Σ +); correlation energies for these systems and for CO were calculated using an atoms-in-molecule approach, relativistic energies and vibrational structure corrections were also considered. The results are: IP(CO, 1σ) = 542.4 (542.57) eV, IP(CO,2σ) = 297.0 (296.24) cV, Dc(CO, 1Σ +) = 10.8 (11.1) Ev, D3(CO +, 1σ, 2Σ +) = 11.9 eV, De(CO +, 2σ, 2Σ +) = 9.1 eV, where IP and De stand respectively for ionization potential and dissociation energy, and where the numbers in parentheses refer to the most recent experimental values. The electron transfers resulting from the ionization of inner-shell electrons are discussed. Finally a quantitative correlation is developed correlating absolute chemical shifts to charge densities. Agreement between the calculated values and those derived from the correlation is quite satisfactory. 相似文献
19.
We study the porphyrin S 1→S 0 fluorescence and the photosensitized singlet oxygen 1Δ g→ 3Σ g phosphorescence, both originating from absorption of photons with energy less than the porphyrin S 0→S 1 transition energy. By measuring the excitation intensity dependence of fluorescence at lowered sample temperatures, we are able to discriminate between two parallel processes of one-photon hot-band absorption (HBA) and simultaneous two-photon absorption (TPA). When the HBA and TPA contributions are comparable in magnitude, we use this new method to determine absolute TPA cross-section. We also demonstrate for the first time a singlet oxygen photosensitization via HBA in porphyrin. 相似文献
20.
By monitoring the green fluorescence transition of mercury vapor 7 3S 1→6 3P 02 (546.074 nm) excited by two pulsed dye lasers tuned at two connected atomic resonant frequencies, i.e. 6 1S 0→6 3P 01 (253.652 nm) and 6 3P 01→ 7 3S 1 (435.835 nm), a decrease in the green fluorescence yield is experimentally observed when the intensity of the 435.835-nm excitation transition exceeds 5 kW/cm 2. A similar result is obtained at the yellow fluorescence transition 6 3D 1→6 1P 01 (578.967 nm) when the second step is tuned to the 6 3P 01→6 3D 1 transition (313.159 nm). At the same time, an increase in the transmittance of the ground state transition (253.652 nm) is observed. It is speculated that this effect, which occurs only when both laser pulses are temporally coincident, and is therefore not due to photoionization, can be ascribed to the existence of laser induced effects, such as a.c. Stark splitting of levels and possibly electromagnetically-induced transparency (EIT). Our experiment does not allow us to distinguish between these two effects, nor their quantitative evaluation. However, it is stressed that one cannot overlook them in those atomic multi-step excitation experiments in low collisional environments where a depletion of an intermediate level is involved, as for example in the case of atomic fluorescence dip spectroscopy or atomic multistep and multiphoton resonance ionization spectroscopy. 相似文献
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