Parameterized effective potential for excited electronic states

The method of the parameterized effective potential (PEP) is developed for constructing the potential curves of excited electronic states of the same symmetry. Unlike the traditional methods of the density functional theory, the PEP is constructed as the direct mapping of an external potential. The PEP generates the one-particle orbitals such that the corresponding single-determinant Kohn-Sham function constructed on their basis is orthogonal to the determinant functions of lower-lying states. A comparison of the potential curves constructed for the HeH and H₂ molecules by the PEP method with the precision data obtained based on the time-consuming configuration interaction methods shows that the PEP method can provide good accuracy for the geometry of an equilibrium configuration and the vertical excitation energies.     

GeCl分子激发态的势能曲线和辐射寿命的理论研究

采用考虑Davidson校正、标量相对论效应、芯-价电子关联和自旋-轨道耦合效应高精度的多参考组态相互作用方法计算了GeCl分子的最低解离极限Ge(3Pg)+Cl(2Pu)对应的12个Λ-S电子态的势能曲线. 基于计算得到的势能曲线, 求解一维核运动的Sch?rdinger方程得出束缚态的光谱常数, 这些光谱常数与实验值符合较好. 本文计算了12个Λ-S态的电偶极矩随核间距的变化, 分析了电子态组态成分的变化对电偶极矩的影响. 本文还研究了GeCl分子的辐射跃迁性质, 给出了激发态到基态之间和低激发态之间的跃迁偶极矩和电子态之间的Franck-Condon因子, 并根据计算得到的跃迁偶极矩和Franck-Condon因子计算出了束缚激发态低振动能级的辐射寿命.     

CARS spectra of thermally excited SF6 molecules

CARS spectra of thev ₁ mode of thermally excited SF₆ were calculated numerically. The influence of the vibrational quasicontinuum on the CARS spectra has been considered by introducing different types of the homogeneous broadening at different vibrational levels. The appearance of additional lines in the CARS spectrum due to mixing of high-lying vibrational levels by Fermi coupling was considered numerically in the frame of a simple model. A comparison of calculated and experimental spectra has been made.     

Renner parameters of isotopic polyatomic molecules

From a consideration of the form of the bending potential in internal coordinates for a ¹Π electronic state of a linear molecule, the equations for calculating the bending vibrational frequencies and Renner parameters of different isotopic molecules are obtained, and relations connecting the Renner parameters of different isotopes are derived. The recent results for the [Gtilde] ¹Π _u and [Htilde] ¹Π _u states of acetylene isotopes [5] are consistent with the theory, but it is not possible at present to determine the sign of ε₅₅ for the [Htilde] ¹Π _u state from the C₂HD isotope effect on ε₄₄.     

Vibrational combination states of polyatomic molecules investigated by ultrashort two-pulse spectroscopy

A first infrared pulse at frequency ν₁ generates transitions to intermediate states in S₀ and a simultaneous visible pulse at ν₂ raises the excited molecules to a state in S₁. Tuning the frequencies ν₁ and ν₂ over several hundred wave numbers and holding the sum ν₁ + ν₂ constant allows the observation of various combination vibrations. The technique is demonstrated on polyatomic molecules consisting of 42 atoms.     

On the determination of small electric dipole moments of excited electronic states in diatomic molecules

A new method is proposed for the determination of small electric-dipole moments in diatomic molecules by measuring the induced transitions due to crossed electric and magnetic fields. A theoretical treatment is given for states belonging to Hund's cases (a) and (b), and for states in the intermediate coupling case between Hund's cases (a) and (b). The method is restricted to non-Σ states.     

Collisional depolarization of fluorescence of polyatomic molecules in the gas phase by excited state quenchers

A new method of extracting information on the efficiencies of quenching of an excited state and collisional reorientation from the data on the fluorescence depolarization of molecular vapors by quenchers of the excited state is proposed. The method does not involve collisional cross sections and fluorescence lifetimes. From the experimental data on the depolarization of polarized luminescence of para-quaterphenyl and 2-(4′-dimethylamine) phenyl-5-phenyloxydiazole by oxygen and nitrogen, the ratios of the constants of the excitedstate quenching and orientation randomization (fluorescence depolarization) by oxygen are obtained. For these molecules, the probabilities of the excited-state quenching q and orientation randomization s per collision with oxygen molecules are determined (q=0.25±0.04 and s=0.13±0.04 for para-quaterphenyl and q=0.2±0.04 and s=0.21±0.04 for 2-(4′-dimethylamine)phenyl-5-phenyloxydiazole). The self-quenching of fluorescence of perylene vapors, with the probability 0.28 per collision, is found.     

BeCl分子电子激发态的多参考组态相互作用计算

运用含Davidson修正的多参考组态相互作用方法,在aug-cc-pVTZ基组水平上,对BeCl分子基态和相同多重度的几个低电子激发态进行了势能扫描计算.通过群论原理确定各电子态对称性及离解极限.将其中基态(X²Σ⁺)和第一激发态(A²Π})对应的势能曲线拟合到Murrell-Sorbie解析势能函数形式,得到基态(X²Σ⁺)的离解能及主要光谱常数(括号中为文献[6]提供的实验值)为D_e=3.74eV,R_e=0.18173nm(0.17970),w_e=857.4cm¹(847.2),w_ex_e=5.03cm^-1(5.14),B_e=0.7103cm^-1(0.7285),α_e=0.0059cm^-1(0.0069),第一激发态(A²Π)的D_e=3.02eV,R_e=0.18369nm(0.18211),w_e=832.7cm^-1(822.1),w_ex_e=5.93cm^-1(5.24),B_e=0.6953cm^-1(0.7094),α_e=0.0065cm^-1(0.0068),计算结果与实验值符合得较好.另外,通过Level程序求解双原子径向核运动的Schrödinger方程得到J=0时BeCl分子这两个电子态的全部振动能级.     

Excitation of polyatomic molecules by radiation

An elementary procedure for calculating quantum mechanically the time-dependent rotation-vibration wave function for a collisionless model of a polyatomic molecule in a monochromatic radiation field is described and applied to some very simple cases. It is concluded that molecules can in principle be strongly and selectively excited at radiation intensities which are too low to produce appreciable excitation in classical calculations. The excitation process is a coherent multi-photon Rabi precession between two discrete levels followed by a transition to a quasi-continuum of vibration-rotation states.     

染料分子电子激发态振动失相过程的非相干光时延四波混频研究

本文对噁嗪(Oxagine)、甲酚紫(cresyl violet)染料分子的吸收带和吸收边进行了非相干光时延四波混频(TDFWM-IL)的详细研究,得到了有关失相参量的数据,并利用非相干光时延四渡混频的多能理论解释了实验结果和失相参量的物理意义。     

Simple models of the density of vibrational states in polyatomic molecules

An analytic approach to calculations of the density of vibrational states in a system consisting of independent anharmonic oscillators was developed. The method worked at all energies from zero point energies to the complete dissociation energies of the selected oscillators.     

A semi-empirical method for the calculation of spin—orbit splitting in degenerate electronic states of linear polyatomic molecules

A semiempirical method for the calculation of spin—orbit coupling constants in linear polyatomic molecules is discussed. The method uses the readily available output from a CNDO/2 calculation and a set of effective atomic coupling constants obtained from observed spectroscopic data on atoms. Two procedures for obtaining the spin—orbit splitting are discussed: one based on a closed shell CNDO/2 calculation and one based on an open shell calculation.The average error for the molecules studied was 6.8% and 7.7% for the two procedures used in the calculations, the easier closed shell procedure giving the lower percentage error. It should be noted that the largest errors occurred in the case of diatomic molecules where the error would be expected to be the greatest. Thus, the average error involved in the values of the spin—orbit splitting for polyatomic molecules is much less than 3.7% for the closed shell procedure. The method used appears to be extendable to non-linear molecules in which the only atoms off the principle symmetry axis of the molecules are hydrogen. The method should be useful in the interpretation of photoelectron spectra.     

Characteristic features of electronic and vibrational spectra of free polyatomic molecules

The functional relationships between the basic characteristics of individual bands of electronic and vibrational spectra of free polyatomic molecules are ascertained. These basic characteristics are the position of the maximum of an individual electronic-vibrational band, the rate of the temperature shift of the maximum of a band, the half-width of a homogeneously or heterogeneously broadened electronic-vibrational band, the rate of the temperature variation of the half-width of a band, the asymmetry parameter of a heterogeneously broadened band, and the conditions for symmetric or asymmetric distribution of the intensity over the contour of a spectral band. The interrelations between the basic spectral characteristics result from the sequential mechanism of formation and broadening of individual bands of electronic and vibrational spectra of free polyatomic molecules. It is shown that the investigation of the basic spectral characteristics of electronic-vibrational bands and their interrelations allows one to elucidate the nature of the internal motion determining the optical properties of polyatomic molecules.     

Quantum-chemical characteristics of the ground and excited electronic states of the isomeric porphycene and porphin molecules

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 2, pp. 282–290, August, 1991.