Electronic Transition Moment Research Articles

Theoretical study with rovibrational and electronic transitionmoment calculation of the ion LiCs+

For the molecular ion LiCs+ the potential energy are calculated for the 39 lowest molecular states of symmetries 2Σ+, 2Π, 2Δ, and Ω = 1/2, 3/2, 5/2. Using an ab initio method, the calculation is based on nonempirical pseudopotentials and parameterized [Formula: see text]-dependent polarization potentials. Gaussian basis sets are used for both atoms and spin-orbit effects are taken into account. The spectroscopic constants for 20 states are calculated by fitting the calculated energy values to a polynomial in terms of the internuclear distance r. Through the canonical functions approach, the eigenvalue Ev, the abscissas of the corresponding turning points (rmin and rmax), and the rotational constants Bv are calculated for up to 44 vibrational levels for four bound states. Using the same approach the dipole moment functions, the corresponding matrix elements, and the transition dipole moments are calculated for the bound states (1)2Σ+, (2)2Σ+, and (1)2Π. The comparison of the present results with those available in literature for the ground state shows a very good agreement. Extensive tables of energy values versus internuclear distance are displayed at the following address: http://lasim.univ-lyon1.fr/allouche/licsso.html.PACS Nos.: 31.15.Ar, 31.25.–v, 31.25.Nj

Franck–Condon factors, transition probabilities, and radiative lifetimes for hydrogen molecules and their isotopomeres

A systematic fundamental molecular database for all isotopomeres of the hydrogen molecule (H 2, D 2, T 2, HD, HT, DT) is calculated on the basis of the latest Born–Oppenheimer potential curves and the latest electronic dipole transition moments of hydrogen molecules. Vibrational eigenvalues, Franck–Condon factors, and vibrationally resolved transition probabilities are presented for electronic transitions in each multiplet system up to principal quantum number n = 4. Radiative lifetimes of the vibrational levels in the electronically excited states are obtained from the summation over the optically allowed transitions. In a similar manner, effective transition probabilities and effective radiative lifetimes of electronically excited states are determined assuming that only the lowest vibrational level in the ground state is populated, i.e. the data are directly applicable to molecular gases. Differences between the isotopomeres are discussed briefly.

Potential energy and transition dipole moment functions of †

The potential energy curves of in its and states are constructed by morphing the appropriate icMRCI ab initio curves within the framework of the Reduced Potential Curve (RPC) approach of Jen[cbreve] and Plíva. The actual morphing is performed by fitting the RPC parameters to available experimental data. The resulting potential energy curves are in close harmony with these data thus allowing for evaluation of highly accurate wavefunctions of the observed rovibronic molecular states and for reliable interpolation of the so-far unobserved states. Using these wavefunctions and theoretically evaluated electronic transition moment functions, the dipole moment matrix elements are calculated for the allowed transitions among the studied vibronic states. The potential energy curve is also used for predicting rotational energies of . The calculated data are believed to be useful in searching for spectral evidence of both in the laboratory and interstellar medium. Several rotational lines of the v = 0 − 1 vibronic band of the B transition are shown to be coincident with absorption features in the spectrum of the carbon star HD 56126. †Dedicated to Professor Andrzej Sadlej on the occasion of his 65th birthday.

Theoretical transition probabilities for the ÃΠ1-X̃Σ+1 system of AlNC and AlCN isomers based on global potential energy surfaces

Transition probabilities were evaluated for the X (1)Sigma(+)-A (1)Pi system of AlNC and AlCN isomers to analyze photoabsorption and fluorescence spectra. The global potential energy surfaces (PESs) of the X (1)Sigma(+) and A (1)Pi (1 (1)A("),2 (1)A(')) electronic states were determined by the multireference configuration interaction calculations with the Davidson correction. Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional PESs of these states and the electronic transition moments for the X-1 (1)A(") and X-2 (1)A(') systems. Einstein's B coefficients obtained for AlNC or AlCN exhibit that the Al-N or Al-C stretching mode is strongly enhanced in the transition. The absorption and fluorescence spectra calculated for the X-1 (1)A(") and X-2 (1)A(') systems are discussed comparing with the observed photoexcitation and fluorescence spectra. The lifetimes for the several vibrational levels of the A (1)Pi state were calculated to be ca. 7 ns for AlNC and 21-24 ns for AlCN from the fluorescence decay rates of the 1 (1)A(")-X and 2 (1)A(')-X emissions.

Arrays of radiative transition probabilities for [formula omitted] plasmas

Franck–Condon factors, Einstein coefficients, and band oscillator strengths have been calculated for the most prominent diatomic radiative transitions found in high-temperature CO 2 – N 2 gases and plasmas. A bibliographic review has allowed selecting the most up-to-date spectroscopic constants, which were used for rebuilding the electronic states potential curves through the Rydberg–Klein–Rees method. Vibrational wavefunctions have been determined for such potential curves and combined with the most up-to-date electronic transition moments found in the literature, in order to determine the transition radiative properties. The proposed set should provide an useful and accurate spectroscopic database for the determination of the radiative properties of CO 2 – N 2 gases and plasmas.

Aggregation of 1,3,7-trimethylxanthine with methylene blue in aqueous solution

We have studied self-association of aromatic molecules of the thiazine dye methylene blue in aqueous solution, using a dimer model. We have determined the dimerization equilibrium constant for the dye molecules KD = 3900 ± 800 M−1 at T = 293 K. We have decomposed the experimental spectrum into dimer and monomer components. Using the ratio of the molar absorption coefficients for two absorption bands of the dimer spectrum, we obtained the “average” value of the angle between the electronic transition moments of the molecules in the dimers, α = 48°. We have studied heteroassociation of methylene blue (MB) and 1,3,7-trimethylxanthine (caffeine) molecules in aqueous solution. We have calculated the heteroassociation constant as 200 ± 34 M−1. We conclude that heteroassociation of methylene blue and caffeine molecules leads to a lower effective dye concentration in solution, which hypothetically may affect its biological activity. We have determined the values of the Gibbs free energy, the enthalpy, and the entropy for dimerization of methylene blue molecules: ΔG293 = −(20 ± 3) kJ/mol, ΔH = −(25 ± 9) kJ/mol, Δ S293 = −(17 ± 6) J/mol·K; and for methylene blue-caffeine heteroassociation: ΔG293 = −(13 ± 3) kJ/mol, ΔH = −(14 ± 10) kJ/mol, ΔS293 = −(2.4 ± 0.2) J/mol·K, respectively. We have shown that the methylene blue aggregates and the heteroassociates with caffeine are predominantly stabilized by dispersion interactions between the chromophore molecules in the associates.

Theoretical Investigation of Doubly Resonant IR−UV Sum-Frequency Vibrational Spectroscopy of Binaphthol Chiral Solution

The doubly resonant IR-UV sum-frequency vibrational spectroscopy (SFVS) of 1,1'-bi-2-naphthol (BN) solution and its dispersion spectra are analyzed and computed using the ZINDO//AM1 calculation and the direct approach of Raman scattering tensor calculation, which is based on calculations of Franck-Condon factors and on differentiation of the electronic transition moments with respect to the vibrational normal modes. The calculated results indicate that, for the most intense vibrational bands observed in the SFVS experiment, the calculated frequencies, symmetry, order, intensities, and pattern of the enhanced vibrational modes agree with experiment qualitatively, and due to the Franck-Condon progression, there are the doublet peaks in the corresponding resonant sum-frequency dispersion spectra. The polarization resonance Raman spectra of BN for the vibrational modes appearing in SFVS are also computed and associated with the experiment SFVS of BN. This direct evaluation approach of Raman tensors may provide a way of assigning the doubly resonant IR-UV SFVS.

High resolution electronic spectra of 7-azaindole and its Ar atom van der Waals complex

Rotationally resolved fluorescence excitation spectra of the S(1)<--S(0) origin band of 7-azaindole [1H-pyrrolo(2,3-b)pyridine] and its argon atom van der Waals complex have been recorded and assigned. The derived rotational constants give information about the geometries of the two molecules in both electronic states. The equilibrium position of the argon atom in the azaindole complex is considerably different from its position in the corresponding indole complex. Furthermore, the argon atom moves when the UV photon is absorbed. There are significant differences in the intermolecular potential energy surfaces in the two electronic states. A large, vibration-state-dependent rotation of the S(1)<--S(0) electronic transition moment vector of 7-azaindole relative to that of indole suggests that these differences have their origin in S(1)/S(2) electronic state mixing in the isolated molecule, a mixing that is enhanced by nitrogen substitution in the six-membered ring.

Interfacial Charge-Transfer Absorption: Semiclassical Treatment

Optically induced charge transfer between adsorbed molecules and a metal electrode was predicted by Hush to lead to new electronic absorption features but has not been experimentally observed. However, Gerischer characterized photocurrents arising from such absorption between adsorbed metal atoms and semiconductor conduction bands. Interfacial charge-transfer absorption (IFCTA) provides information concerning the barriers to charge transfer between molecules and the metal/semiconductor and the magnitude of the electronic coupling and could thus provide a powerful tool for understanding interfacial charge-transfer kinetics. Here we provide a framework for modeling and predicting IFCTA spectra. The key feature of optical charge transfer to or from a band of electronic levels (taken to have a constant density of states and electronic coupling element) is that the absorption probability reaches half intensity at lambda + DeltaG(theta), where lambda and DeltaG(theta) are the reorganization energy and free-energy gap for the optical charge transfer, attains >90% intensity at lambda + DeltaG(theta) + 0.9 square root[4lambdak(B)T], and remains essentially constant until the top (bottom) level of the band is attained. However, when the electronic coupling and transition moment are assumed to be independent of photon energy (Mulliken-Hush model), a peaked, highly asymmetric absorption profile is predicted. We conclude that, in general, the electronic coupling between molecular adsorbates and the metal levels is so small that absorption is not detectable, whereas for semiconductors there may be intense features involving coupling to surface states.

Vibrational energies for the X̃A11, ÃB11, and B̃A11 states of SiH2∕SiD2 and related transition probabilities based on global potential energy surfaces

Transition probabilities were evaluated for the X(1)A(1)-A(1)B(1) and A(1)B(1)-B(1)A(1) systems of SiH(2) and SiD(2) to analyze the X-->A-->B photoexcitation. The Franck-Condon factors (FCFs) and Einstein's B coefficients were computed by quantum vibrational calculations using the three-dimensional potential energy surfaces (PESs) of the SiH(2)(X(1)A(1),A(1)B(1),B(1)A(1)) electronic states and the electronic transition moments for the X-A, X-B, and A-B system. The global PESs were determined by the multireference configuration interaction calculations with the Davidson correction and the interpolant moving least-squares method combined with the Shepard interpolation. The obtained FCFs for the X-A and A-B systems exhibit that the bending mode is strongly enhanced in the excitation since the equilibrium bond angle greatly varies with the three states; the barrier to linearity is evaluated to be 21,900 cm(-1) for the X state, 6400 cm(-1) for the A state, and 230-240 cm(-1) for the B state. The theoretical lifetimes for the pure bending levels of the A and B states were calculated from the fluorescence decay rates for the A-X, B-A, and B-X emissions.

A Theoretical Study for the Valence−Rydberg Interaction in Diatomic Molecules. Application to the NO β Band System

A detailed description of the β band system of the NO molecule has been achieved by calculating electronic transition moments, Einstein coefficients, and radiative lifetimes. The known strong interaction of the B 2 ∏ valence state with Rydberg states of 2 ∏ symmetry is treated through a vibronic interaction matrix. This actually implies an extension of the molecular quantum defect orbital (MQDO) methodology in the study of vibronic levels of diatomic molecules. The MQDO approach has recently led to rather good results in the study of the 3sσ(A 2 Σ + )-X 2 ∏ (y band), 3pσ(D 2 Σ + )-X 2 ∏ (∈ band), and 3pσ(D 2 E + )-3sσ(A 2 Σ + ) transitions.

Electronic transition moment with spin‐orbit coupling of the molecular ion KRb+

AbstractBy using the electronic wave functions obtained from an ab initio calculation, including the spin‐orbit coupling, the electronic transition moments have been investigated for two bound states of symmetry Ω = 1/2 and Ω = 3/2 of the molecular ion KRb+. Based on a canonical functions approach for the determination of the vibrational wave functions, the matrix elements have been calculated for the bound states considered for v = 0, 10, 20 with v′‐ v = 0, 1, 2, …, 6; by using the same canonical approach, the eigenvalues and abscissas of the corresponding turning points (rmin and rmax) have been investigated for these states that obtained from a theoretical ab initio calculation up to v = 105. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005

Rovibrational distribution determination of H2 in low temperature plasmas by Fulcher-α band spectroscopy

It is proposed that the rotational and vibrational temperatures of H2 can be derived from the fitting to the H2 Fulcher band line emissions. However, the fitting relies on the employed spontaneous radiative transition probabilities and the excitation rate coefficients, which are dependent on the vibrational and rotational quanta in each electronic state. From our study, it is found that, in low temperature plasmas both the Fulcher-α radiative transition and the electron impact excitation to the d 3 Πu state from the ground electronic state deviate significantly from the Franck–Condon approximation. The vibrationally resolved complete sets of the cross sections are calculated based on the semi-classical Gryzinski theory, and the Fulcher band transition probabilities are obtained based on the newest published data on the electronic transition moment and the solution to the radial Schrödinger equation. The fitting to experimental line emissions shows that Boltzmann's Law can be employed for the distribution of vibrational (in lower level), and particularly for the rotational, populations in the ground electronic state of H2 in low temperature plasmas.

Vibronic transition moments and line intensities for H 2O +

Ab initio calculations of the electronic dipole moment components for the A ̃ 2A 1 and X ̃ 2B 1 electronic states and the electronic transition moment for the A ̃ 2A 1 – X ̃ 2B 1 transition of H 2O + have been carried out. Parameterized analytical functions have been fitted through the computed ab initio data points, and the resulting dipole moment and transition moment surfaces have been used, along with potential energy surfaces derived from the ab initio results of Brommer et al. [J. Chem. Phys. 98 (1993) 5222], to simulate H 2O + spectra and to generate an extensive set of vibronic transition moments for the A ̃ – X ̃ and X ̃ – X ̃ band systems of H 2O +. The work is made with the dual purpose of facilitating further assignments of high-resolution spectra [J. Mol. Spectrosc. 219 (2003) 258] and of allowing cometary spectra of H 2O + to be simulated [Ap. J. 574 (2002) L183].

Resonance Raman Intensity Analysis of Merocyanine Dimers in Solution

Resonance Raman excitation profiles and absolute cross sections are presented for three closely related merocyanine dyes as monomers in dichloromethane solution and as H-dimers in dioxane solution. For both monomers and dimers the absorption spectra and the resonance Raman intensities of the 24 to 30 strongest vibrations are quantitatively simulated using time-dependent wave packet propagation methods to determine the geometry changes along each Franck−Condon active mode upon electronic excitation, as well as the homogeneous and inhomogeneous electronic line widths. In addition, an approach previously formulated to describe the vibronic structure of an excitonically coupled homodimer with multiple vibrational modes [Kelley, A. M. J. Chem. Phys. 2003, 119, 3320−3331] is applied to model the dimer spectra. Comparison of these two calculations demonstrates that when the intermonomer coupling is strong the theoretical absorption and resonance Raman spectra of the dimer can be very well approximated by treating the system as a “supermolecule” having a single electronic transition with appropriately rescaled vibrational displacements, transition dipole, and electronic zero−zero frequency. The experimental dimer spectra exhibit the reduced Franck−Condon activity expected from distributing the electronic excitation over two monomers. However, deviations in the intensity patterns for individual vibrations suggest additional, more specific effects of dimerization, and the electronic transition moment for the lowest allowed transition of the monomer is not conserved upon dimer formation. An excitonically coupled monomer model therefore appears inadequate to describe the electronic excitations in these strongly coupled noncovalent dimers.

Extension of the molecular quantum defect orbital methodology to the calculation of intensities and lifetimes for vibronic transitions within electronic Rydberg series of NO

AbstractExpressions relating explicitly the radiative lifetimes of vibronic states to the electronic transition moment and the absorption oscillator strengths for spin‐allowed transitions have been developed for the first time within the molecular quantum defect orbital (MQDO) methodology. Application to the intensities of the γ(A2Σ+ ← X2Π), ε(D2Σ+ ← X2Π), and (D2Σ+ ← A2Σ+) bands of NO, which are known to be of relevance in atmospheric studies, has been made. The MQDO results are in excellent accord with the measurements available in the literature. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2004

Photodissociation dynamics of 1-propanol and 2-propanol at 193.3 nm

193.3-nm photodissociation dynamics of jet-cooled 1-propanol and 2-propanol and their partially deuterated variants are examined by using the high-n Rydberg-atom time-of-flight technique. Isotope labeling studies show that O–H bond fission is the primary H-atom production channel in the ultraviolet photodissociation of both 1-propanol and 2-propanol. Center-of-mass (c.m.) product translational energy release of the RO–H dissociation channel is large, with 〈fT〉=0.78 for H+1-propoxy (n-propoxy) and 0.79 for H+2-propoxy (isoproxy). Maximum c.m. translational energy release yields an upper limit of the O–H bond dissociation energy: 433±2 kJ/mol in 1-propanol and 435±2 kJ/mol in 2-propanol. H-atom product angular distribution is anisotropic (with β≈−0.79 for 1-propanol and −0.77 for 2-propanol), suggesting an electronic transition moment perpendicular to the H–O–C plane and a short excited-state dissociation lifetime (less than a rotational period). Information about photodissociation dynamics and bond energies of the partially deuterated propanols are also obtained. The 193.3-nm photodissociation dynamics of 1-propanol and 2-propanol are nearly identical to each other and are similar to those of methanol and ethanol. This indicates a common RO–H dissociation mechanism: after the nO→σ*(O–H)/3s excitation localized on the H–O–C moiety, the H atom is ejected promptly in the H–O–C plane in a time scale shorter than a rotational period of the parent molecule, and it dissociates along the O–H coordinate on the repulsive excited-state potential-energy surface with a large translational energy release.

High resolution absorption spectrum of jet-cooled OCS between 64 000 and 91 000 cm−1

The absorption spectrum of jet-cooled OCS was photographed from 190 to 110 nm at a resolution limit of 0.0008 nm. No band maximum was observed between 190 and 156 nm, i.e., below 64 000 cm−1. Ab initio calculations of the electronic energies and transition moments were carried out, including spin–orbit interaction, in the frozen core approximation. Rydberg states considered have ionic core X̃ 2Π and principal effective quantum number n*=2–5.5, electronic angular momentum l=0–5. Up to n*=3.5, l=0–2, calculations were also done in the coupled electron pair approximation. It is shown that in OCS, like in N2O, CO2 or CS2, npπ 1Σ+ states are at lower energy than npσ1,3Π. From the doublet structure shown by the corresponding transition origin bands, the rotational constant of the 4pσ1,3Π and 4pπ 3Σ− states was deduced to be B0′=0.1940(5) cm−1. Transitions involving excitation to ns or nd Rydberg orbitals, allowed in the less-symmetric molecules, were calculated to have relative intensities respectively two and three orders of magnitude greater in OCS than in N2O. The ns series could be assigned only to medium intensity or weak bands. In contrast, ndδ1Π transitions were assigned to relatively strong bands and could be followed up to n about 20. Previous low-resolution absorption and electron-impact spectra are reviewed. Most of the present assignments agree with those of resonance enhanced multiphoton ionization spectra and satisfactory assignments are obtained for the 15 unassigned electronic origins observed by Morgan et al. [J. Chem. Phys. 105, 2141 (1996)].

Dependence of the electronic transition moment for the C 3Δ–X 3Δ system of TiO on the internuclear distance

Intensity distributions of eight vibronic bands associated with v ′=0–3 for the C 3Δ–X 3Δ transition of TiO were observed by dispersed emission spectroscopy, and the variation of the electronic transition moment, R e( r), for the C 3Δ–X 3Δ system was determined as a function of the internuclear distance r; R e (r)∝{1−2.04(31)(r−r 0)+195(43)(r−r 0) 3} (r 0=1.65869 A ̊ and 1.59130 A ̊ ⩽r⩽1.71214 A ̊ ). This r-dependence of R e ( r) is discussed in terms of the polarization in the unpaired 10 σ orbital.

The near-threshold absorption spectrum of N2

A new comprehensive multichannel quantum defect study of the near-threshold absorption of N214 has been carried out over the energy range 118 720–125 425 cm−1. A nearly complete understanding of the rotationally cold spectra reported earlier [K. P. Huber and Ch. Jungen, J. Chem. Phys. 92, 850 (1990); K. P. Huber et al., ibid. 100, 7957 (1994)] has been achieved in the region where core-excited s and d Rydberg levels built on the A 2Πu state of the ion interact with the series of p and f complexes converging to the lowest vibrational levels of X 2Σg+. The interactions reduce to a purely electronic quantum defect matrix which, after suitable transformations, accounts for the observed perturbed structures and intensities arising from vibronic coupling, rotational l uncoupling, and the different geometries of the X and A ion cores. The final calculations converged with 42 nonzero quantum defect parameters reproducing the 597 upper-state rovibronic levels with a standard deviation of 1.12 cm−1. The results have been used to calculate the R(0) line oscillator strengths in terms of eight nonvanishing electronic dipole transition moments, the latter treated as parameters that were fitted to photoelectrically measured band absorption f values. The calculations satisfactorily reproduce the observed oscillator strength distribution. Using ab initio calculated core properties for ground state N2+, the long-range model for a nonpenetrating Rydberg electron interacting with a quadrupolar and polarizable ion core predicts the diagonal f quantum defects in reasonable agreement with the results of the least-squares fits. Similar to NO, deviations from predictions by the same model for the diagonal d quantum defects arise primarily from the strong sσ∼dσ interchannel coupling and from the intrachannel interaction of the dπg Rydberg with the 1πg valence orbital, which, in contrast to 2π of NO, is occupied not in the ground state of N2, but in the electronically excited precursor states a′ 1Σu−, w 1Δu, and b′ 1Σu+.