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1.
The equilibrium geometries, excitation energies, force constants and vibrational frequencies for seven low-lying electronic states X 1A1, 1B1, 3B1, 1A2, 3A2, 1B2 and 3B2 of dichlorocarbene CCl2 have been calculated at the MRSDCI level with a double-zeta plus polarization basis set. Our calculated equilibrium geometry for the X 1A1 state, excitation energy for X 1A11B1 and vibrational frequencies for the X 1A1 and 1B1 states are in good agreement with experimental data. The electronic transition dipole moments, oscillator strengths for the 1B1 → X 1A1 and 1B2 → X 1A1 transitions, radiative lifetimes for the 1B1 and 1B1 states are calculated using MRSDCI wavefunctions, predicting results in reasonable agreement with experiment.  相似文献   

2.
The 12B1(X2B1), 12B2, 12A1, 12A2, 22B2, and 22A1 states of the ion were studied using CASPT2 and CASSCF methods. Calculations suggest that one should consider the 32A′ state instead of 22B2. The CASPT2 T0 calculations predict the energy ordering of 12B1(X2B1), 12B2, 12A1, 12A2, 32A′, and 22A1, which is in line with the experimental results by Pradeep and Shirley. The CASPT2 T0 values for the 12B2, 12A2, 32A′, and 22A1 states are close to the experimental values. The F-loss and H-loss dissociation processes were studied at the CASPT2//CASSCF level. The energy levels of low-lying states of are compared.  相似文献   

3.
用YAG四倍频激光把SO2分子从电子基态X1A1激励到电子激发态A1A2和B1B1的高振动耦合区, 获得了320~380um范围内SO2(B1B1→X1A1)的激光诱导荧光色散谱, 并给出初步标识;提出一个三能态模型来处理266nm激光激励的SO2(X1A1, A1A2, B1B1)体系的态间转移, 并获得了A态和B态在高振动能区的耦合系数ξ及耦合达到动态平衡的弛豫时间τ, 发现二者反映的是被研究体系的固有特性, 与提出的模型吻合.  相似文献   

4.
The threshold electron impact excitation spectrum of ketene is reported. The spectrum is interpreted in comparison with results of an ab initio frozen core calculation. Triplet states (3A2, 3A1, 3B1) are observed at 3.8, 5.0 and 5.8 eV excitation energy.  相似文献   

5.
We have combined the high sensitivity of the ICLAS technique with the rotational cooling effect of a slit jet expansion in order to observe and to understand the visible and near infrared NO2 spectrum. By this way, an equivalent absorption pathlength of several kilometers through rotationally cooled molecules has been achieved. Due to the vibronic interaction between the two lowest electronic states, 2A1 and à 2B2, this spectrum is vibronically dense and complex. Moreover, the dense room temperature rotational structure is perturbed by additional rovibronic interactions. In contrast, the rotational analysis of our jet cooled spectrum is straightforward. The NO2 absorption spectrum is vanishing to the IR but, owing to the high sensitivity of the ICLAS technique, we have been able to record the NO2 spectrum down to 11200 cm−1 with a new Ti:sapphire ICLAS spectrometer. As a result 249 2B2 vibronic bands have been observed (175 cold bands and 74 hot bands) in the 11200–16150 cm−1 energy range. Due to the cooling effect of the slit jet we have reduced the rotational temperature down to about 12 K and at this temperature the K = 0 subbands are dominant. Consequently, we have analysed only the K = 0 manifold for N 7 of each vibronic band. The dynamical range of the band intensities is about one thousand. Due to the strong vibronic interaction between the 2A1 and à 2B2 electronic states, we observed not only the a1 vibrational levels of the à 2B2 state but also the b2 vibrational levels of the 2A1 state interacting with the previous ones. By comparison with the calculated density of states, we conclude that we have observed about 65% of the total number of 2B2 vibronic levels located in the studied range. However, there are more missing levels in the IR because of the weakness of the spectrum in this range. The correlation properties of this set of vibronic levels have been analysed calculating the power spectrum of the absorption stick spectrum which displays periodic motions: the dominant period, at 714 ± 20 cm−1, corresponds to the bending motion of the à 2B2 state. The other observed periods remain unassigned. In contrast the next neighbor spacing distribution (NNSD) shows a strong level repulsion, i.e. a manifestation of quantum chaos. These two observations, apparently contradictory, can be rationalized as follows: the short time dynamics, for t < 10−12 s, is “regular” while for longer times the dynamics becomes “chaotic”. We suggest that this behavior may be observed directly with a pump and probe fs laser experiment.  相似文献   

6.
Bo-Zhen Chen  Ming-Bao Huang   《Chemical physics》2004,300(1-3):325-334
In the present theoretical work we have explored mechanisms of dissociation reactions of the vinyl radical in the A2A″ state (C2H3 (A2A″)) and examined possible pathways for nonadiabatic dissociation of C2H3 (A2A″) into C2H2 (X1Σg+). 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 C2H3 in the A2A″ state were explored: (1) C2H3 (A2A″) → C2H2 (trans, 3Au) + H, (2) C2H3 (A2A″) → C2H2 (cis, 3A2) + H, and (3) C2H3 (A2A″) → H2CC (3A2) + H. The CASSCF and CASPT2 potential energy curve calculations for the C2H3 (A2A″) 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 C2H3 (A2A″) into C2H2 (X1Σg+) + 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 C2H3 (A2A) structure might be feasible. The CASSCF/cc-pVTZ geometry optimization and frequency analysis calculations were performed for the four C2v bridge structures in the 2B2, 2A2, 2B1, and 2A1 states along the pathways of the 12A (X2A), 12A″ (A2A″), 22A″, and 22A states of C2H3, respectively, and the CASPT2//CASSCF/cc-pVTZ energetic results indicate that the assumed IC pathway, via a C2v (2A2) structure and then 2A2/2A1 surface crossing, be not feasible since at their excitation wavelengths (327.4 and 366.2 nm) the C2v (2A2) structure could not be accessed.  相似文献   

7.
Relative emission spectra for the bent to linear, CO2(1B2)---CO2(X1Σ+g) transitions have been calculated using the model: harmonic oscillator, symmetric-top wavefunctions and energy levels for CO2(1B2); first-orer Fermi resonance vibrational wavefunctions and energy levels for CO2(X1Σ+g); a Boltzmann distribution of vibrational and rotational states in CO2(1B2); and a constant electronic transition moment. With the literature CO2(1B2) molecular structure, spectra calculated using this model show characteristics similar to the low-temperature chemiluminescence from the combination of atomic oxygen and carbon monoxide. The calculated spectra account for experimental band positions to wavelengths of 570 nm and the weak dependence of the spectra on temperature over the range 206–353 K. The latter result was obtained from a CO2(1B2) bending fundamental of 600 cm−1. The calculated spectra also show a violet-shift in intensity and an attenuated band structure at higher temperatures. The magnitude of these effects depends on the CO2(1B2) force constants and not on the CO2(1B2) molecular structure.  相似文献   

8.
We present extensive MRD CI ab initio calculations for the first two excited states of 1A″ symmetry (1B1 and 1A2 in the C2v point group). Full three-dimensional potential energy surfaces are constructed by varying both H---S-bond lengths as well as the HSH bending angle. The lower adiabatic potential is dissociative whereas the upper one is binding. These surfaces, together with the transition dipole moments with the ground electronic state, form the basis for future investigations of the photodissociation of hydrogen sulfide.  相似文献   

9.
The photoabsorption spectrum of ozone in the UV range (5–9 eV) is calculated from a short-time wave packet propagation using six potential energy surfaces obtained from ab initio electronic structure calculations. It is shown that the (unnamed) band around 7 eV, which is immediately adjacent to the intense Hartley band, is primarily due to excitation of three electronic states: 5 1A′ (3 1A1), 6 1A′ (4 1A1), and 4 1A″ (2 1B1). Excitation of the state 8 1A′ (1B2) leads to a broad and intense band starting around 8 eV with a maximum near 9.1 eV. In full accord with the recent experimental study of Brouard et al. [M. Brouard, R. Cireasa, A.P. Clark, G.C. Groenenboom, G. Hancock, S.J. Horrocks, F. Quadrini, G.A.D. Ritchie, C. Vallance, J. Chem. Phys. 125 (2006) 133308], the excitation at 193 nm (6.42 eV) involves at least two states (5 1A′ and 4 1A″) different from the state excited in the Hartley band (3 1A′). The dynamics along the dissociation path is discussed in terms of one-dimensional potential curves. Several avoided crossings among the excited 1A′ as well as the 1A″ states point to a complicated fragmentation process. Although a quantitative analysis of branching ratios is not possible on the basis of the present calculations, we surmise, that in addition to and O(1D) + O2(1Δg), the next higher spin-allowed channel, , also is likely to be a major product channel, in agreement with experimental observations.  相似文献   

10.
Resonance fluorescence spectra of CF2(1B1, 040, K' = 9) excited at 253 7 nm have been observed in the photolysis of C2F4 using a low-pressure mercury lamp. At low C2F4 pressures, the spectra with a series of doublet hands from 254 to 400 nm were consistent with the transitions from 1B1, 040, K'=9 to 1A1, 0v'20, K' = 8, 10, and also to 1A1, 1v'20, K' = 8, 10 The appearance of doublet bands (Δ K = ±1) provides clear evidence that the transition is of the perpendicular type.  相似文献   

11.
The mechanism of the H2NO(2B1)→NO(2Π)+H2 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 H2NO(2B1). It is therefore considered that trajectories that start from H2NO(2B1) 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)+H2. Thus we can explain the mechanism of the H2NO(2B1)→NO(2Π)+H2 reaction, which has remained unclear to date.  相似文献   

12.
Summary Ab initio calculations have been performed to study on the molecular structures and the vibrational levels of the low-lying ionic states (2A2 and2B1) of furan. The equilibrium molecular structures and vibrational modes of these states are presented. The theoretical ionization intensity curves including the vibrational structures of the low-lying two ionic states are also presented and compared with the photoelectron spectrum. A number of new assignments of the photoelectron spectra are proposed.  相似文献   

13.
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 11Ag → 11B2u and 11Ag → 11B3u 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 11Ag → 21B1u, 11Ag → 21B3u and 11Ag → 21B2u 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   

14.
MCSCF and MRCI calculations on the first three singlet states of trans-1,3-butadiene are presented. Flexible basis sets were applied and full geometry optimization was carried out at the MCSCF level for planar and selected non-planar structures including twisting and pyramidalization of terminal CH2-groups. Geometry relaxations in and excitation energies to 1 1Bu and 2 1Ag states are discussed in detail. For planar structures the covalent 2 1Ag state is lower in energy than the 1 1Bu state. If non-planar geometry relaxations are allowed, the lowest lying non-planar excited singlet state turns out to be ionic with one terminal CH2 group rotated by 90°. Limitations of the current investigations due to restrictions in the MRCI treatment and because of incomplete scanning of excited state surfaces are pointed out.  相似文献   

15.
A complete vibrational analysis has been carried out for 10B2O3, 11B2O3, and sulfur dicyanide and a set of molecular constants, i.e. kinetic constants, potential constants, compliance constants, vibrational mean amplitudes, Coriolis coupling constants and centrifugal distortion constants, is reported. The values of the centrifugal distortion constants of S(CN)2, are in good agreement with the observed values, which bears out the significance of the method of kinetic constants adopted in this work.  相似文献   

16.
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 A1+B1+3pB2. Correlated to excited states of benzene, the results show that A1+B1 corresponds to 1E1u and 3pB2 to 3p 1A2u. It indicates that the double degeneracy of 1E1u state does not yet degrade in p-fluorotoluene. Moreover, it occasionally degenerates with 3p1 A2u. Furthermore, the electron distribution in the phenyl ring maintains the symmetry of the D6h point group consistently like in benzene.  相似文献   

17.
应用密度泛函B3LYP方法和从头算(abinitio)HF方法,在3-21G理论水平上,对具有C2v,D2d,D3h和D6h对称性的四种C36异构体以及在保持D2d,D3h和D6h对称性条件下形成的不同氢化物进行了量子化学计算,研究了它们在不同量子态时的分子几何构型和电子结构.结果表明,电子相关效应在C36簇化合物的电子结构中起着重要作用.它们最稳定的结构是C363A2u量子态D6h异构体,而C36的氢化物是在D3h异构体的C2位置等同碳原子上形成的1A1'量子态氢化物C36H12.  相似文献   

18.
J. Troe 《Chemical physics》1995,190(2-3):381-392
Numbers and densities of vibrational states of non-rotating polyatomic molecules are calculated by a simplified model which accounts for Morse anharmonicities of stretching and for generalized empirical stretch-bend couplings of bending modes. At energies above the dissociation limit, adiabatic channel maxima restrict the molecular phase space. The model is applied to the NO2( 2A1), NO22B2), and H3+ systems for which satisfactory agreement with the available experimental or calculational results is obtained.  相似文献   

19.
 Ab initio calculations have been performed to study the molecular structures and vibrational levels of the four low-lying ionic states (1, 22Π, and 1, 22Σ+) of carbonyl sulfide. The global regions of the potential-energy surfaces have been obtained by multireference single and double excitation configuration interaction calculations. Vibrational calculations using explicit vibrational Hamiltonians have been used for vibrational analysis. The equilibrium molecular structures and a vibrational analysis of the four ionic states are presented. The theoretical ionization intensity curves including the vibrational structures of the ionic states are also presented and are compared with the photoelectron spectrum. Received: 20 January 2001 / Accepted: 22 August 2001 / Published online: 30 October 2001  相似文献   

20.
Semiempirical self-consistent field (SCF) and configuration interaction (CI) calculations of the intermediate neglect of differential overlap (INDO) type are applied to the analysis of the electronic transitions of the hexaazacyclophane base and its Ni and Cu complexes. The ground states (1Ag for the ligand and Ni complex, 2B1g for the Cu complex) are planar structures of D2h symmetry. The low-energy region of the UV-visible spectra, whose analysis may help to recognize the catalytic active sites of the complexes is associated with d → d transitions in the Ni complex, and M → L charge transfer in the Cu complex.  相似文献   

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