Calculation of electric dipole transition moments using quasi-degenerate variational perturbation theory and averaged coupled-pair functional theory

Results are reported from calculations of electric dipole transition moments for various electronic transitions in Be, CH₂, and A1H using multireference singles and doubles configuration interaction, quasi-degenerate variational perturbation theory, and multireference averaged coupled pair functional theory. A simple normalization scheme is used for the quasi-degenerate variational perturbation theory and multireference averaged coupled pair functional theory wave functions. In all cases, comparison is made with full configuration interaction results in the valence space. For Be and CH₂, all methods are of comparable quality in calculating the transition moments and excitation energies, with averaged coupled-pair functional theory yielding slightly quicker convergence of the excitation energies and transition moments in most cases. For AlH, multireference singles and doubles configuration interaction is somewhat more accurate for the calculation of the transition moment. Factors that affect the accuracy of the methods are discussed. © 1994 John Wiley & Sons, Inc.     

A method for the calculation of transition moments between electronic states of molecules using a different one-electron basis set for each state

A state-specific approach to the calculation of transition moments between molecular electronic states requires that the wavefunction for each state is expanded in its optimum one-electron basis and that nonorthonormal basis techniques are used for the calculation of the transition moment integrals. A method has been developed for carrying out such nonorthonormal basis calculations, based on the corresponding orbitals transformation and appropriately defined density matrices, which may be used with configuration interaction (CI ) wavefunctions. Further improvements of the method have resulted in a decrease in the time required for the calculations and thus allow its application with moderately large CI expansions for each state. Nonorthonormal basis calculations on transition moments in H₂O have been carried out using the above method. The results are in agreement with those of large MRD -CI calculations.     

Comparisons of the RPA,SCRPA, Tamm–Dancoff,and full CI methods by analysis of their transition density matrices,oscillator strengths,and energy moments of oscillator strengths for the electric dipole transitions from the ground state of the B+ ion (frozen K-shell model)

The RPA, SCRPA , Tamm–Dancoff, and full CI methods are compared by analyzing their transition density matrices, oscillator strengths, and energy moments of oscillator strengths for the ¹S_ground – ¹P_odd transitions of the 4-electron B⁺ ion in the frozen K-shell approximation. It is found that the RPA gives transition density matrices that are aligned nearly as well as possible along those of the full CI , but have vector lengths that are significantly too long. The corresponding transition energies are significantly too small. These errors compensate to give oscillator strengths for the dominant transition that, for all forms of the oscillator strength, are within 1.6% of the corresponding full CI values. The SCRPA gives better transition density matrices than the RPA , but poorer oscillator strengths. The Tamm-Dancoff approximation gives very good values for the mixed length-velocity form of the oscillator strength. The RPA gives a static electric dipole polarizability that is nearly 20% larger than that of the full CI . The SCRPA gives a value 15% smaller than—and the Tamm-Dancoff approximation gives a mixed length-velocity value that is 11% larger than—that of the full CI . Other energy moments of oscillator strengths are also reported. Certain other approximations related to the RPA and the SCRPA are reported as well.     

An investigation of vibrational exciton bands in solid nitrous oxide

Infrared spectra of N₂O crystals containing dilute to isotopic impurities are reported. Information on the second moments and other properties of the vibrational exciton bands has been determined from an analysis of the impurity modes, the LOTO splittings, and a comparison of the transition dipole moments of N₂O with those of CO₂. The effect of the random sense of the molecules on the spectra is discussed.     

Rotational—vibrational dipole transitions in HD

The transition moments are computed for several lines in the X¹Σ⁺_g state of HD. The results are obtained by taking into account interactions with Σ_u and Π_u states. It is shown that the latter influence appreciably the transition probabilities in the 00 band. The permanent dipole moment is also computed for several vibrational and rotational states.     

Photophysical Properties of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine

Spectral and photophysical investigations of 4′-(p-aminophenyl)-2,2′:6′,2′′-terpyridine (APT) have been performed in various solvents with different polarity and hydrogen-bonding ability.The emission spectra of APT are found to exhibit dual fluorescence in polar solvents, which attributes to the local excited and intramolecular charge transfer states, respectively. The two-state model is proven out for APT in polar solvent by the time-correlated single photon counting emission decay measurement. Interestingly, the linear relationships of different emission maxima and solvent polarity parameter are found for APT in protic and aprotic solvents, because of the hydrogen bond formation between APT and alcohols at the amino nitrogen N25. Furthermore, the effects of the complexation of the metal ion with tpy group of APT and the hydrogen bond formation between APT with methanol at the terpyridinenitrogen N4—N8—N14 are also presented. The appearance of new long-wave absorption and fluorescence bands indicates that a new ground state of the complexes is formed.     

Photochemical and photophysical study on the kinetics of the atmospheric photodissociation of acetone

The pressure dependence of the photodissociation quantum yield of acetone has been determined in different buffer gases at 308 nm. Results by Stern-Volmer analyses are in accordance with a suggested photolysis mechanism. Luminescence spectra, lifetimes and transition dipole moments have been determined. The energy transfer process by O₂ to give O₂(¹Δ_g) is of minor importance in the case of the singlet excited state of acetone, while it is the dominant deactivation process for the triplet state.     

Effects of the dipole moments behavior on a vibronic coupling model for the four‐wave mixing signal

In the present work, we have studied modifications in the transition and permanent dipole moments of states in a coupled basis (including vibronic coupling) due to variations in the transition dipole moment between the uncoupled states, m₁₂, as a function of the parameter δ = ₀/ω₀ (relative aperture) of the potential‐energy curves of the states involved. Modifications in the slopes of the transition and permanent dipole moments of the coupled states and changes in the magnitude of maximal intensity of the four‐wave mixing (FWM) signal are observed due to variations in these parameters. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004     

Absorption spectrum of flexible conjugated polymers: the weak-disorder limit

Purely conformational contributions to dipole transition moments lead to a general new expression for the absorption spectrum of flexible conjugated polymers with persistence length ξ_c and alternation δ. Blue-shifts are found at rod-to-coil transitions without invoking rotational defects that break the conjugation. Conformational coupling in the weak-disorder limit increases the effective alternation.     

A theoretical investigation of the excited states of the H2O2 molecule

Ab initio calculations for a series of excited states of the H₂O₂ molecule have been performed in order to discuss some recent photofragmentation experiments with laser light. For understanding these experiments the direction of the transition moments is of great interest, as well as the possibility of a HOO…H fragmentation.     

Trends for intensities of vibrational overtones in methane

The concept of local vibrational modes is examined quantitatively for spherical-top molecules. New theoretical formulations of transition electric dipole moments are developed for diatomics and local-mode spherical tops. Transition moments inferred from high-resolution spectra of ν₃, 2ν₃ and 3ν₃ in ¹²CH₄ and ¹³CH₄ constitute the data base from which comparisons between theory and experiment, and predictions, are made.     

Optical rotatory strength calculation by evaluating the gradient matrix through the equation of motion

A straightforward generalization of Linderberg's equation-of-motion-based formula for the matrix elements of the linear momentum operator is proposed. The essential feature of the modification is the abandonment of the zero differential overlap (ZDO) approximation for the electric transition integrals. It is expected that this new formula gives better transition moments and, consequently, better optical rotatory strength values. The results of this modification are analysed numerically for the rotatory strengths of the twisted hydrogen peroxide and for the 1,6-diazaspiro[4,4]-nonane-2,7-dione, C₇H₁₀N₂O₂, molecule, using a CNDO Hamiltonian. For both systems a definitive improvement of calculated rotatory strengths resulted.     

The use of the CNDO method in spectroscopy

The Pariser approximation for the two center Coulomb repulsion integrals Γ _rshas been replaced by the Nishimoto-Mataga approximation in the original CNDO/S method. This modification has significantly improved the calculated position of the benzene ¹ B _1u ←¹ A _1g(¹ L _a ) electronic transition in benzenoid compounds. The calculation of transition moments of n — π ^* transitions is also considered. These moments vanish formally in any theory employing the ZDO approximation since integrals of the form 〈2s¦er2p〉 vanish even when the 2s and 2p atomic orbitals are on the same center. In this work the ZDO approximation is abandoned in the evaluation of the electronic transition moment resulting in calculated intensities for n — π ^*, ¹W←¹A, transitions which are in good agreement with experiment.     

Omuralide and Vibralactone: Differences in the Proteasome‐ β‐Lactone‐γ‐Lactam Binding Scaffold Alter Target Preferences

Despite their structural similarity, the natural products omuralide and vibralactone have different biological targets. While omuralide blocks the chymotryptic activity of the proteasome with an IC₅₀ value of 47 nM, vibralactone does not have any effect at this protease up to a concentration of 1 mM . Activity‐based protein profiling in HeLa cells revealed that the major targets of vibralactone are APT1 and APT2.     

Spectroscopic properties of the methyl radical calculated from UHF SCEP wavefunctions

The potential energy surface of symmetric stretching and out-of-plane bending motions for the methyl radical has been calculated from UHF SCEP wavefunctions. Anharmonic vibrational frequencies are computed by a variational method and transition dipole moments and Einstein coefficients of spontaneous emission are reported. Isotropic hyperfine coupling constants are obtained in agreement with experiment to within 4% when calculated by differentiation of the perturbed CEPA-1 energy and taking vibrational averaging into account. Also, the temperature dependence of the proton hyperfine coupling constant compares well with experimental results. The vibrational fine structure of the first band of the photoelectron spectra of CH₃ and CD₃ is calculated in good agreement with experiment.     

Spectrophotometric investigation on the aggregation in water of some benzothiazole cationic dyes

The aggregation ability in water of some practically important benzothiazole diazahemicyanine dyes in the range, where only the monomer-dimer equilibrium exist, is investigated. The equilibrium constants K_D and thermodynamic parameters of dimerization are determined and their influence on the dye aggregation is discussed. The “sandwich” structure of the dimer is suggested from the pure monomer and dimer absorption spectra. The distance R between the molecules in the dimer and the angle α between the two transition dipole moments are determined.     

Vibronic coupling calculation of the pre-resonance Raman intensities of naphthalene

The relative enhancement of the Raman intensities in the pre-resonance region has been computed for naphthalene, using the vibronic coupling expansion proposed by Albrecht. The relevant vibronic and transition moments have been computed in the CNDO/S approximation, while the normal coordinates of naphthalene have been evaluated using a MINDO/3 program. The experimental pattern of intensities is reproduced in a satisfactory way both for b_3g and a_g vibrations. The most important states and the main vibronic terms in the expansion are individuated and discussed with respect to the vibronic borrowing present in the Fluorescence spectrum of naphthalene.     

Molecular structure and microbiological activity of alkali metal 3,4-dihydroxyphenylacetates

The changes in physical, chemical and biological properties of chemical compounds decide about their biological activity. In this paper the molecular structure of alkali metal 3,4-dihydroxyphenylacetates is studied in comparison to 3,4-dihydroxyphenylacetic acid (3,4-DHPAA) using FT-IR, FT-Raman and UV–Vis spectroscopy as well as density functional theory (DFT) calculations. The B3LYP/6-311++G⁷ method is used to calculate optimized geometrical structures of studied compounds, atomic charges (Mulliken, APT, NBO), dipole moments, energies as well as the wavenumbers and intensities of the bands in vibrational spectra. Theoretical parameters are compared to the experimental data. The relationship between spectroscopic parameters of studied compounds and their biological activity is analyzed. Antioxidant activity is studied using FRAP and DPPH methods. IC₅₀ parameter is also calculated. Bacillus subtilis, Pseudomonas aeruginosa, Escherichia coli and Klebsiella oxytoca are used in microbiological analysis of 3,4-DHPAA as well as its sodium and potassium salts.     

Spectrometric study of the interaction between Alpinetin and bovine serum albumin using chemometrics approaches

The binding interaction of Alpinetin (APT) with bovine serum albumin (BSA) was studied by fluorescence, UV-visible and synchronous fluorescence spectroscopy (SFS) under simulated physiological conditions. The measured complex spectra were resolved by multivariate curve resolution-alternating least squares (MCR-ALS), yielding a host of data and information, which otherwise would have been impossible to obtain. The extracted profiles corresponded to the spectra of the single species in the APT/BSA mixture. In addition, the presence of the APT-BSA complex was demonstrated, and it was shown that the associated quenching of the fluorescence from the BSA protein resulted from the formation of APT-BSA complex via a static mechanism. The binding constant (K_a(ave) = 2.34 × 10⁶ L mol⁻¹) and the number of sites (n = 1) were obtained by fluorescence methods as were the thermodynamic parameters (ΔH⁰, ΔS⁰ and ΔG⁰). This work suggested that the principal binding between APT to BSA was facilitated by hydrophobic interactions. The thermodynamic parameters for APT were compared to those from the structurally similar Chrysin and Wogonin molecules. It appeared that the entropy parameters were relatively more affected by the small structural changes. SFS from the interaction of BSA and APT showed that the ligand affected the conformation of BSA. The competitive interaction of APT and site makers with BSA indicated site I as the binding area of APT in BSA.     

Quantification of dopant species using atom probe tomography for semiconductor application

Doping of semiconductors serve various purposes in metal-oxide-semiconductor (CMOS) technology, eg, increase carrier concentration and modify electric field distribution. With the scaling down of device and the introduction of three-dimensional fin field-effect transistors (FinFET), precise and reliable dopant quantification of concentration at the nano-scale is critical. Laser-assisted atom probe tomography (APT) provides a unique approach to characterize and quantify the dopant in three dimensions at sub-nanometer resolution. Nevertheless, quantification accuracy of APT is strongly influenced by the experimental conditions. Although B quantification has been widely studied, the correlation of B signal loss to B concentration is not yet established. In addition, no phosphorous quantification study has been reported. In this work, we found that, due to B multi-hit effect in APT, high B dose sample has larger B loading compared with low B dose sample. For standard calibration with minimized impact from multi-hit effect, we recommend B dose in the range of 1e14 atoms/cm². Despite the fact that B loading is dose dependent, APT quantification of B achieves precision within 2% to 6% relative standard deviation (RSD), which demonstrates that APT has good accuracy. On the other hand, P quantification suffers from mass interference of ³¹P⁺ and ³¹P₂²⁺ at 31 Da resulting in a large loading between APT and secondary ion mass spectrometry (SIMS). Nevertheless, we recommend that 31 Da to be labeled as ³¹P⁺ for smaller P variation for the APT analysis.