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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.
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
3.
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
4.
Gaussian-2 ab initio calculations were performed to examine the six modes of unimolecular dissociation of cis-CH 3CHSH + (1 +), trans-CH 3CHSH + (2 +), and CH 3SCH 2+ (3 +): 1 +→CH 3++ trans-HCSH (1); 1 +→CH 3+ trans-HCSH + (2); 1 +→CH 4+HCS + (3); 1 +→H 2+ c-CH 2CHS + (4); 2 +→H 2+CH 3CS + (5); and 3 +→H 2+ c-CH 2CHS + (6). Reactions (1) and (2) have endothermicities of 584 and 496 kJ mol −1, respectively. Loss of CH 4 from 1 + (reaction (3)) proceeds through proton transfer from the S atom to the methyl group, followed by cleavage of the C–C bond. The reaction pathway has an energy barrier of 292 kJ mol −1 and a transition state with a wide spectrum of nonclassical structures. Reaction (4) has a critical energy of 296 kJ mol −1 and it also proceeds through the same proton transfer step as reaction (3), followed by elimination of H 2. Formation of CH 3CS + from 2 + (reaction (5)) by loss of H 2 proceeds through protonation of the methine (C H) group, followed by dissociation of the H 2 moiety. Its energy barrier is 276 kJ mol −1. On both the MP2/6-31G* and QCISD/6-31G* potential-energy surfaces, the H 2 1,1-elimination from 3 + (reaction (6)) proceeds via a nonclassical intermediate resembling c-CH 3SCH 2+ and has a critical energy of 269 kJ mol −1. 相似文献
5.
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
6.
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
7.
Saddle point geometries and barrier heights have been calculated for the H abstraction reaction HO 2( 2A″)+H( 2S) → H 2( 1Σ +g)+O 2( 3Σ −g) and the concerted H approach-O removing reaction HO 2 ( 2A″)+H( 2S) → H 2O( 1A 1)+O( 3P) by using SDCI wavefunctions with a valence double-zeta plus polarization basis set. The saddle points are found to be of C s symmetry and the barrier heights are respectively 5.3 and 19.8 kcal by including size consistent correction. Moreoever kinetic parameters have been evaluated within the framework of the TST theory. So activation energies and the rate constants are estimated to be respectively 2.3 kcal and 0.4×10 9 ℓ mol −1 s −1 for the first reaction, 20.0 kcal and 5.4.10 −5 ℓ mol −1 s −1 for the second. Comparison of these results with experimental determinations shows that hydrogen abstraction on HO 2 is an efficient mechanism for the formation of H 2 + O 2, while the concerted mechanism envisaged for the formation of H 2O + O is highly unlikely. 相似文献
8.
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
9.
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
10.
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
11.
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
12.
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
13.
The electric field gradients (EFG’s) at the nucleus are calculated as a function of internuclear separation in the X 2Σ g+ and B 2Σ u+ electronic states of the nitrogen molecule cation using the internally contracted multireference configuration interaction (icMRCI) method. The EFG’s and potential energy functions (PEF’s) are used to estimate the 14N nuclear quadrupole coupling constants (NQCC’s) in the two electronic states as functions of vibrational and end-over-end rotational quantum numbers. The dependences of the computed constants on the basis set and reference configuration space are investigated. Since no counterpart for comparison of the calculated NQCC’s exists, the N 2+ results are supported by analogous calculations on the X 1Σ g+ and A 3Σ u+ states of N 2, for which established data are available. The overall good quality of the icMRCI wave functions is further corroborated by a favorable agreement of spectroscopic constants derived from the corresponding PEF’s and experimental data. Variations of the EFG with internuclear separation are explained in terms of wave function composition, and used for gaining specific insight into the chemical bonding in N 2+ and N 2. 相似文献
14.
N 2O gas phase chemistry has been examined as it relates to the problem of ultrathin film silicon oxynitridation for semiconductor devices. Computational and analytical kinetics studies are presented that demonstrate: (i) there are 5 main reactions in the decomposition of N 2O, (ii) the gas composition over a 1000K – 1400K temperature range is as follows: N 2 (65.3 − 59.3%); O 2 (32.0 − 25.7%); NO (2.7 − 15.0%), (iii) the N 2O decomposition obeys first-order kinetics, and the initial rate law for N 2O decomposition is R init = 2k 1[N 2O] which rapidly changes to R late = k 1[N 2O] as the reaction proceeds, (iv) the branching ratio for the two reactions: N 2O + O → 2NO and N 2O + O → N 2 + O 2 lies between 0.1 and 0.5 (0.1 < < 0.5) and varies with conditions, (v) the apparent activation energy for the decomposition of N 2O is 2.5 eV/molecule (2.4×10 2 kJ/mole), (vi) the rate law for NO formation is R = k 1N 2O], and (vii) the apparent activation energy for the formation of NO is 2.4 eV/molecule (2.3×10 2 kJ/mole). 相似文献
15.
Reactions of excited NH(a 1Δ) with C 2H 6 have been investigated. Reactions proceed via three pathways: (a) insertion of NH (a 1Δ) into a C-H bond, (b) abstraction of H, and (c) electro me quenching of NH (a 1Δ). From the pressure dependence of yields of the insertion product (C 2H 5NH 2) and fragmentation products (C 2H 5 and CH 3, the branching ratios were determined to be 0.6 for (a), 0.1 for (b) and 0.3 for (c). 相似文献
16.
Potential curves were calculated for eighteen low-lying doublet and quartet states of PN +, using configuration-interaction methods and double-zeta plus polarization and diffuse basis sets. Spectroscopic constants were evaluated for fourteen stable states. The X 2Σ + ground state lies very close to A 2Π (0.34 eV calculated). The 2 2Σ + state has two shallow minima of similar energy, being due to σ* → σ at smaller R, and π → π* at larger R. For N 2+, σ* → σ is much lower in energy than π → π*, whereas the opposite situation applies to P 2+. 相似文献
17.
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
18.
Rotational-state distributions of the CO + (A–X, B–X) and N 2+(B–X) emissions produced by the collisions of He(2 3S) with CO and N 2 were studied in the collision energy ( ER range 100–200 meV. The rotational populations of the emitting states can be fitte by single Boltzmann temperatures ( TR. The TR (320 ± 30 K) for the ν′ = 3 and 4 levels of the CO + (A 2Π) state are nearly independent of, or slightly increase with, ER, while TR for the CO +(B 2Σ +, ν′ = 0) state increases rapidly with ER.The TR (430 ± 20 K) for the N 2+(B 2Σ +, ν′ = 0) state is nearly independent or slightly decreases with increasing ER. Interactions providing these trends are discussed. 相似文献
19.
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A 2A″ state (C 2H 3 (A 2A″)) and examined possible pathways for nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+). In the calculations we used the complete active space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods in conjunction with the cc-pVDZ and cc-pVTZ basis sets. Mechanisms for the following three dissociation channels of C 2H 3 in the A 2A″ state were explored: (1) C 2H 3 (A 2A″) → C 2H 2 ( trans, 3A u) + H, (2) C 2H 3 (A 2A″) → C 2H 2 ( cis, 3A 2) + H, and (3) C 2H 3 (A 2A″) → H 2CC ( 3A 2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C 2H 3 (A 2A″) dissociation channels (1)–(3) indicate that there is neither transition state nor intermediate for each of the channels. At the CASPT2//CASSCF/cc-pVTZ level, the dissociation energies for channels (1)–(3) are predicted to be 84.3, 91.1, and 86.9 kcal/mol, respectively. For a recently observed nonadiabatic dissociation of C 2H 3 (A 2A″) into C 2H 2 (X 1Σ g+) + H [J. Chem. Phys. 111 (1999) 3783], two previously suggested internal conversion (IC) pathways were examined based on our CASSCF and CASPT2 calculations. Our preliminary CASSCF and CASPT2 calculations indicate that the assumed IC pathway via the twisted C 2H 3 (A 2A ′) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C 2v bridge structures in the 2B 2, 2A 2, 2B 1, and 2A 1 states along the pathways of the 1 2A ′ (X 2A ′), 1 2A″ (A 2A″), 2 2A″, and 2 2A ′ states of C 2H 3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C 2v ( 2A 2) structure and then 2A 2/ 2A 1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C 2v ( 2A 2) structure could not be accessed. 相似文献
20.
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
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