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1.
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
2.
Intense red emission peaking at 703 nm is observed when a heated metal wire is placed downstream of an O 2( 1Δ g) generator used in the chemical oxygen iodine laser (COIL) system. The O 2( 1Δ g) is produced by bubbling Cl 2 through an alkaline solution of H 2O 2. Evidence is presented that strong red emission requires the presence of both O 2( 1Δ g) and Cl 2 in contact with a heated metal surface. Several metals have been used. The red emission spectrum is independent of the metal and the intensity is strongest for copper. 相似文献
3.
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
4.
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
5.
The mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction has been examined using ab initio molecular orbital methods. Ground-state and first-excited-state potential surfaces were plotted at the FOCI/cc-pVTZ level of theory as functions of two appropriate internal degrees of freedom. A conical intersection was found on the Cs pathway that is symmetric with respect to the plane perpendicular to the molecular plane of C2v H 2NO( 2B 1). It is therefore considered that trajectories that start from H 2NO( 2B 1) towards the product region detour around the conical intersection, pass through the neighborhood of the transition state that is located at the saddle point on the Cs pathway, and finally reach the products, NO( 2Π)+H 2. Thus we can explain the mechanism of the H 2NO( 2B 1)→NO( 2Π)+H 2 reaction, which has remained unclear to date. 相似文献
6.
A Doppler-based velocity selection technique has been used to measure the relative velocity dependence of the cross sections σ ji,Δ(ν r) for rotationally inelastic collisions from level ji to ji + Δν 1 = 8,22,42) in 7Li *2 A 1Σ +u)—Xe. The σ jν±2(ν r) are strongly attenuated at a smaller ν r by “torque averaging” due to molecular rotation; in contrast, for large |Δ|, σ jiΔ = ν r−n (1 n 2). An empirical intermolecular potential which reproduces these types of behavior for 3-D classical trajectories is exhibited. 相似文献
7.
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
8.
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
9.
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
10.
The cross section for the quenching of NH(c 1Π, ν = 0) by HN 3 was measured by using a pulsed laser technique. A single rotational level of NH(c 1Π, ν = 0) was formed by exciting NH(a 1Δ, ν = 0) with a frequency doubled dye laser. NH(a 1Δ) was produced by photolyzing HN 3 with a XeCl excimer laser. The time profiles of the NH(c-a) fluorescence were measured at various pressures of HN 3. Experiments were performed both in the presence and in the absence of He buffer gas. In the absence of He, the NH radicals were found to be translationally hot; the average velocity was 3800±600 m s −1. The quenching cross sections for the translationally hot and thermalized NH(c) radicals by HN 3 were determined to be (28±5) × 10 −16 and (85±3) × 10 −16 cm 2, respectively. No rotational level dependence could be observed in the quenching of the hot NH(c) radicals. 相似文献
11.
The low lying electronic states of the molecule MoN were investigated by performing all electron ab initio multi-configuration self-consistent-field (CASSCF) calculations. The relativistic corrections for the one electron Darwin contact term and the relativistic mass-velocity correction were determined in perturbation calculations. The electronic ground state is confirmed as being 4∑ −. The chemical bond of MoN has a triple bond character because of the approximately fully occupied delocalized bonding π and σ orbitals. The spectroscopic constants for the ground state and ten excited states were derived. The excited doublet states 2∑ −, 2Γ, 2Δ, and 2∑ + are found to be lower lying than the 4Π state that was investigated experimentally. Elaborate multi-configuration configuration-interaction (MRCI) calculations were carried out for the states 4∑ − and 4∏ using various basis sets. The spectroscopic constants for the 4∑ − ground state were determined as re=1.636 Å and ω e=1109 cm −1, and for the 4∏ state as re=1.662 Å and ω e=941 cm −1. The values for the ground state are in excellent agreement with available experimental data. The MoN molecule is polar with a charge transfer from Mo to N. The dipole moment was determined as 2.11 D in the 4∑ − state and as 4.60 D in the 4∏ state. These values agree well with the revised experimental values determined from molecular Stark spectroscopic measurements. The dissociation energy, De, is determined as 5.17 eV, and D0 as 5.10 eV. 相似文献
12.
The triplet state ( 32T) and the radical cation (2T +√) of 2,2′-bithiophene (2T) are characterized by pulse radiolysis in CCl 4. Two main absorption bands at 360 and 420 nm are respectively attributed to 32T* and to 2T +√. The triplet, induced in an excited state through a Förster mechanism, undergoes a conformational rearrangement ( k6=(6.8±0.9)×10 6 s −1). The radical cation is produced both through a resonance charge transfer and a second diffusional process; the two oxidizing species are respectively CCl 4+√ and (CCl +3Cl −) solv through the mediation of a singlet excited state, 12T*. 相似文献
14.
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
15.
The phophorescence of biacetyl induced by an energy transfer to biacetyl from triplet benzene produced in the pulse radiolysis of benzene-biacetyl mixtures has been studied. The time required to reach the maximum intensity of phosphorescence, tmax, after the electron pulse, varies as a function of biacetyl pressure at constant benzene pressure (40 torr), which gives the lifetime of triplet benzene τ = (6.7 ± 3.2) × 10 −6 s and the rate constant of the energy transfer kC6H6*(T1) + biacetyl = (1.6 ± 0.7) × 10 −10 cm 3 molecule −1 s −1. 相似文献
16.
Large-scale MRD CI calculations assign to AlP the ground state X 3Σ − (9σ 23π 2) and a close-lying state 1 3Π (9σ3π 3) ( Te = 0.08 eV). Up to transition energies of 2.0 eV, other states are described by the configurations 9σ3π 3 (1 1Π), 8σ 23π 4 (1 1Σ +), 9σ 23π 2 (1 1Δ and 2 1Σ +) and 9σ3π 24π (1 5Π). The 2 3Π state, located at ≈ 2.30 eV, shows a shallow double minimum. Numerous perturbations are expected to induce predissociation upon 2 3Π. Multiplets arising from the occupation 8σ 23π 34π are clustered in the 3.25–3.50 eV region. Quintet states with the configuration 8σ9σ3π 34π are bound, with Te values (in eV) of 3.80 (1 5Σ +), 4.44 (1 5Δ) and 4.88 (3 5Σ −), respectively. The 9σ → 4s Rydberg members 5Σ − and 3Σ − lie in the 4.58–4.72 eV energy region. The first ionization potential (ionization to X 4Σ − of AlP +, 9σ → ∞) is estimated to be 7.65 eV. Ionization to the 1 2Σ − and 1 2Π states of AlP + is suggested to occur between 8.0 and 8.8 eV. The dipole moments of X 3Σ −, 1 1Δ and 2 1Σ + are close to 1.0 D, whereas the 1 1Σ + state has μ = 3.49 D; 1 3Π and 1 1Π have dipole moments from 2.45 to 2.91 D. All low-lying states show a polarity Al +P −. Finally, the electronic structure and transition energies of AlP are compared with those of the isoelectronic species BN, AIN, and SiP +. 相似文献
17.
Medium-resolution spectra of the N 2 b 1Π u-X 1Σ g+ band system were recorded by 1 + 1 multiphoton ionization. In the spectra we found different linewidths for transitions to different vibrational levels in the b 1Π u state: Δν 0 = 0.50 ± 0.05 cm −1, Δν 1 = 0.28 ± 0.02 cm −1, Δν 2 = 0.65 ± 0.06 cm −1, Δν 3 = 3.2 ± 0.5 cm −1, Δν 4 = 0.60 ± 0.07 cm −1, and Δν 5 = 0.28 ± 0.02 cm −1. From these linewidths, predissociation lifetimes τ ν were obtained: τ 0 = 16 ± 3 ps, τ 1 > 150 ps, τ 2 = 10 ± 2 ps, τ 3 = 1.6 ± 0.3 ps, τ 4 = 9 ± 2 ps, and τ 5 > 150 ps. Band origins and rotational constants for the b 1Π uν = 0 and 1 levels were determined for the 14N 2 and 14N 15N molecules. 相似文献
18.
Predissociation of the A 2Σ + state is treated by an exact theory employing two frame transformation matrices, each of which connects the atomic term limits (O( 3P) and O( 1D)) to the correlating adiabatic Born—Oppenheimer states. Resonances corresponding to the higher ( v 7) rovibrational levels of the A 2Σ + state are predicted to have asymmetric (Fano-type) profiles. The branching ratios of O( 3P j, J = 0, 1, 2) are shown to be influenced by nonadiabatic interactions in the Franck—Condon region between the A 2Σ + and dissociative 4Σ −, 2Σ − and 4Π states. The branching ratios show a strong variation along asymmetric resonances, while remaining energy independent along Lorentzian resonances. 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.
The absorption spectrum of the benzene—oxygen contact complex from 2350 to 2120 Å has been derived from the difference in the absorption spectra of benzene vapour (70 torr) in the presence and absence of oxygen (760 torr). The complex has an absorption maximum at 2190 Å (5.65 eV), corresponding to a formation energy of 0.42 eV from 1B 1U benzene and 3Σ −g oxygen, and of 2.90 eV from the benzene cation and oxygen anion. The excited complex has an electric dipole length of 5.0 Å. The data are compared with those for benzene complexes with other electron acceptors. 相似文献
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