Diamagnetic Raman Optical Activity of Chlorine,Bromine, and Iodine Gases

Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties. Magnetic Raman optical activity has recently been observed in a paramagnetic gas (Angew. Chem. Int. Ed. 2012 , 51, 11058; Angew. Chem. 2012 , 124, 11220). In diamagnetic molecules, it has been considered too weak to be measurable. However, in chlorine, bromine and iodine vapors, we could detect a significant signal as well. Zeeman splitting of electronic ground‐state energy levels cannot rationalize the observed circular intensity difference (CID) values of about 10^?4. These are explicable by participation of paramagnetic excited electronic states. Then a simple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is a general event observable under resonance conditions. The phenomenon sheds new light on the role of excited states in the Raman scattering, and may be used to probe molecular geometry and electronic structure.     

Combination of Resonance and Non-Resonance Chiral Raman Scattering in a Cobalt(III) Complex

Resonance Raman optical activity (RROA) spectra with high sensitivity reveal details on molecular structure, chirality, and excited electronic properties. Despite the difficulty of the measurements, the recorded data for the Co(III) complex with S,S-N,N-ethylenediaminedisuccinic acid are of exceptional quality and, coupled with the theory, spectacularly document the molecular behavior in resonance. This includes a huge enhancement of the chiral scattering, contribution of the antisymmetric polarizabilities to the signal, and the Herzberg-Teller effect significantly shaping the spectra. The chiral component is by about one order of magnitude bigger than for an analogous aluminum complex. The band assignment and intensity profile were confirmed by simulations based on density functional and vibronic theories. The resonance was attributed to the S₀→S₃ transition, with the strongest signal enhancement of Raman and ROA spectral bands below about 800 cm⁻¹. For higher wavenumbers, other excited electronic states contribute to the scattering in a less resonant way. RROA spectroscopy thus appears as a unique tool to study the structure and electronic states of absorbing molecules in analytical chemistry, biology, and material science.     

Resonance Raman Spectroscopy,and Its Application to Inorganic Chemistry. New Analytical Methods (27)

Resonance Raman spectra are obtained when the wave number of the exciting radiation is close to, or coincident with, that of an electronic transition of the scattering species. Such spectra are usually characterized by a very large enhancement of the intensities of particular Raman bands, sometimes with the appearance of intense overtone and combination tone progressions. The technique provides detailed information about excited electronic states because it is only the vibrational modes associated with the chromophore that are resonance-Raman active. Additionally, the high sensitivity is such that compounds at concentrations as low as 10^?6 mol/L may be detected, enabling resonance Raman spectroscopy to be used as an analytical tool and for the study of chromophores in molecules of biological interest.     

Ferromagnetism, paramagnetism, and thermally induced magnetism in photomagnetic CrIII/MnII and CrIII oxalates with the 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f]quinolinium cation

Single crystals of the new cationic chromene, 7-methyl-3,3-diphenyl-3H-pyrano[3,2-f-quinolinium iodide (C₂₅H₂₀NO)I (1), were synthesized. The crystal structure of the new compound was studied, and quantum chemical calculation for the open and closed forms were carried out. The bifunctional compounds containing mono- and bimetallic 3d metal (tris)oxalates with the chromenium cation, (C₂₅H₂₀NO)₃[Cr(C₂O₄)₃] · 4H₂O (2) and (C₂₅H₂₀NO)[CrMn(C₂O₄)₃] · H₂O (3), were prepared. Compound 1 is paramagnetic due to low-lying thermally excited states of the chromene molecules. At low temperatures (∼2 K), the paramagnetic states are frozen, and the compound becomes diamagnetic. Compound 2 is paramagnetic and its magnetic properties are determined mainly by the Cr³⁺ ions and the thermally induced paramagnetic states of the chromene molecules. At high temperatures, the magnetic moment of compound 3 consists of the contributions of the paramagnetic Cr³⁺ and Mn²⁺ ions and the thermally induced paramagnetic states of chromenes. At low temperatures (2–3 K), the thermally induced magnetism of organic molecules is frozen, and the magnetically ordered (and, probably, spin-glass) state is observed in the two-dimensional network of metal oxalates (T _c = 3 K in the zero magnetic field). The UV irradiation leads to an increase in the magnetic moment of the compound in the paramagnetic region due to the generation of radiation defects.     

Molecular electric properties in electronic excited states: multipole moments and polarizabilities of H2O in the lowest1 B 1 and3 B 1 excited states

Summary The dipole and quadrupole moments and the dipole polarizability tensor components are calculated for the¹ B ₁ and³ B ₁ excited states of the water molecule by using the complete active space (CAS) SCF method and an extended basis set of atomic natural orbitals. The dipole moment in the lowest¹ B ₁ (0.640 a.u.) and³ B ₁ (0.416 a.u.) states is found to be antiparallel to that in the ground electronic state of H₂O. The shape of the quadrupole moment ellipsoid is significantly modified by the electronic excitation to both states investigated in this paper. All components of the excited state dipole polarizability tensor increase by about an order of magnitude compared to their values in the ground electronic state. The present results are used to discuss some aspects of intermolecular interactions involving molecules in their excited electronic states.     

Raman spectroscopy from a picosecond-lived excited state of methyl orange

Vibrational Raman scattering from a picosecond-lived excited state of methyl orange in 9 N H₂SO₄ is reported. The vibrational frequencies of normal modes in ground and electronic excited states are separated by ≈ 10 cm^?1 but rather large differences exist in their intensities. In particular, the intensity of a mode at ≈ 1180 cm^?1, due to the NN stretch, is sensitive to the frequency of the nanosecond pulsed tunable laser. A bandwidth comparison between ground- and excited-state spectra reveals that the widths of bands of the latter, like that of the former are due to dephasing and other effects associated with interaction of molecules in the liquid phase.     

Optical Spectroscopy of the Au4+ Cluster: The Resolved Vibronic Structure Indicates an Unexpected Isomer

Knowledge of the geometric and electronic structure of gold clusters and nanoparticles is vital for understanding their catalytic and photochemical properties at the molecular level. In this study, we report the vibronic optical photodissociation spectrum of cold and mass‐selected Au₄⁺ clusters measured at a resolution high enough to allow for comparison with Franck–Condon simulations of the excited state transitions based on time‐dependent density functional theory calculations. The three vibrational frequencies identified for the lowest‐lying optically accessible excited state at 2.17 eV stem from the Y‐shaped isomer (C_2v) and not from the rhombic isomer (D_2h) considered to be the ground state structure of Au₄⁺. This study demonstrates that an analysis of low‐resolution electronic spectra by calculations of vertical transitions alone is not sufficient for a reliable isomer assignment of such metal clusters.     

Structure and spectra of the molecules of manganese, iron, and cobalt trifluorides: A CCSD(T) study in the complete basis set

The coupled-cluster singles and doubles with perturbative triples (CCSD(T)) method in triple-, quadruple-, and quintuple-zeta basis sets with extrapolation to the complete basis set limit is used to analyze the properties of MnF₃, FeF₃, and CoF₃ molecules. The relative energies of low-lying electronic states are determined. The Jahn-Teller effect is investigated in the ground electronic state ⁵ E?? of the MnF₃ molecule and the first excited electronic state ⁵ E?? of the CoF₃ molecule. Geometric parameters, atomization enthalpies, vibrational frequencies, intensities in the infrared and Raman spectra are found with high accuracy. The assignment of the bands observed in the low-frequency region of the IR and Raman spectra of MnF₃ and CoF₃ molecules are revised.     

Thermoemission of singlet oxygen and chemical structure of copper oxides

Thermal treatment of copper oxides (CuO, Cu₂O) is accompanied by large-scale emission of singlet oxygen molecules (¹Σ⁺ _g ). Electron spectroscopy for chemical analysis (ESCA) and electronic and IR spectroscopy were used to show that the thermoemission of electronically excited molecules results from dark generation of electronically excited states which contain in their structure isolated metal-metal bonds and oxygen associates. The anomalous diamagnetic response of the samples and reduced thermoemission activity (Cu₂O) are associated with cooperative interaction of electronically excited states.     

Raman excitation profiles and excited state molecular configurations of three isomeric phenyl pyridines

Contributions of different electronic states to Raman scattering have been studied by critical analyses of Raman excitation profiles (REPs) of several normal modes of vibration of three isomeric phenyl pyridines. In this context, possible structures and other interesting properties of the three molecules in the excited electronic states have been discussed. Normal mode characteristics are also described. Most likely a singlet state, lying in the vacuum ultraviolet region with respect to the ground state, is found to be playing a very significant role in the scattering phenomena.     

One‐electron pseudopotential study of the alkali hydride cation NaH+: Structure,spectroscopy, transition dipole moments,and radiative lifetimes

The structure and spectroscopic properties of the ground and the lowest excited electronic states of the alkali hydride cation NaH⁺ have been investigated using an ab initio approach. In this approach, a nonempirical pseudopotential for the Na⁺ core has been used and a core–core and a core‐valence correlation corrections have been added. The adiabatic potential energy curves and the molecular spectroscopic constants for numerous electronic states of ²Σ⁺, ²Π, and ²Δ symmetries, dissociating up to Na (4d) + H⁺ and Na⁺ + H (3d), have been calculated. As no experimental data are available, we discuss our results by comparing with the available theoretical calculations. A satisfying agreement has been found for the ground state with previous works. However, a clear disagreement between this study and the model potential work of Magnier (Magnier, J. Phys. Chem. A 2005, 109, 5411) has been observed for several excited states. Numerous avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries have been found and analysed. They are related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Na⁺H and NaH⁺. Furthermore, we provide an extensive set of data concerning the transition dipole moments from X²Σ⁺ and the 2²Σ⁺ states to higher excited states of ²Σ⁺ and ²Π symmetries. Finally, the adiabatic potential energy curves of the ground (X²Σ⁺) and the first (2²Σ⁺) excited states and the transition dipole moments between these states are used to evaluate the radiative lifetimes for the vibrational levels of the 2²∑⁺ state for the first time. In addition to the bound–bound contribution, the bound‐free term has been evaluated and added to the total radiative lifetime. © 2012 Wiley Periodicals, Inc.     

Pyrene‐Based Dyad and Triad Leading to a Reversible Chemical and Redox Optical and Magnetic Switch

Two new pyrene–polychlorotriphenylmethyl (PTM) dyads and triads have been synthesized and characterized by optical, magnetic, and electrochemical methods. The interplay between the different electronic states of the PTM moiety in the dyads and triads and the optical and magnetic properties of the molecules have been studied. The electronic spectra of the radicals 5 ^. and 6 ^. show the intramolecular charge‐transfer transition at around 700 nm due to the acceptor character of the PTM radical. In the diamagnetic protonated derivatives 3 and 4 the fluorescence due to the pyrene is maintained, whereas in the radicals 5 ^. and 6 ^. and the corresponding anions 5 ^? and 6 ^? there is a clear quenching of the fluorescence, which is more efficient in the case of radicals. The redox activity of PTM radicals that are easily reduced to the corresponding carbanion has been exploited to fabricate electrochemical switches with optical and magnetic response.     

Quantum Chemical Study of the Pressure-dependent Phosphorescence of [Cr(ddpd)2]3+ in the Solid State

The chromium(III) complex [Cr(ddpd)₂][BF₄]₃ shows two spin-flip emission bands in the near-infrared spectral region. These bands shift bathochromically by −14.1 and −7.7 cm⁻¹ kbar⁻¹ under hydrostatic pressure (Angew. Chem. Int. Ed. 2018 , 57, 11069). The present study elucidates the structural changes of the chromium(III) cations under pressure using density functional theory with periodic boundary conditions and the resulting effects on the excited state energies using high-level CASSCF-NEVPT2 calculations. The differences of the bands in pressure sensitivity are traced back to a different orbital occupation of the intraconfigurational excited states.     

Theoretical study of low‐lying electronic states of the LiRb+ molecular ion: Structure,spectroscopy and transition dipole moments

The electronic structure and the spectroscopic properties for low‐lying electronic states of the LiRb⁺ molecular ion, dissociating into Li (2s, 2p, 3s, 3p, 3d, 4s, and 4p) + Rb⁺ and Li⁺ + Rb (5s, 5p, 4d, 6s, 6p, 5d, and 7s), have been investigated using an ab initio approach based on non‐empirical pseudo potentials for the Li and Rb cores and parametrized l‐dependent polarization potential. We have determined the adiabatic potential energy curves and their spectroscopic constants for many electronic states of ²Σ⁺, ²Π, and ²Δ symmetries. A satisfying agreement, for the spectroscopic constants, has been obtained for the ground and the first excited states with the available theoretical works. Potential energy curves were presented, for the first time, for the higher excited states. In addition, we have localised and analysed the avoided crossings between electronic states of ²Σ⁺ and ²Π symmetries. Their existences can be related to the interaction between the potential energy curves and to the charge transfer process between the two ionic systems Li⁺Rb and LiRb⁺. Moreover, we have determined the transition dipole moments from X²Σ⁺ and 2²Σ⁺ states to higher excited states of ²Σ⁺ and ²Π symmetries. For our best knowledge, no experimental data on the LiRb⁺ molecular ion is available. These theoretical data can help experimentalists to optimize photoassociative formation of ultracold LiRb⁺ molecular ion and their longevity in a trap or in an optical lattice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Resonance Raman and resonance hyper-Raman intensities: structure and dynamics of molecular excited states in solution

Resonance Raman scattering is discussed as a vibronic spectroscopy that can provide detailed information about the structure and dynamics of excited electronic states of molecules. The emphasis is on molecules in liquid solution. The theory of resonance Raman intensities and experimental and interpretive methods are discussed both in a historical context and in their present and future implementations. The related but much less developed technique of two-photon-resonant hyper-Raman scattering is also discussed in a similar context.     

β‐Carotene Revisited by Transient Absorption and Stimulated Raman Spectroscopy

β‐Carotene in n‐hexane was examined by femtosecond transient absorption and stimulated Raman spectroscopy. Electronic change is separated from vibrational relaxation with the help of band integrals. Overlaid on the decay of S₁ excited‐state absorption, a picosecond process is found that is absent when the C₉‐methyl group is replaced by ethyl or isopropyl. It is attributed to reorganization on the S₁ potential energy surface, involving dihedral angles between C₆ and C₉. In Raman studies, electronic states S₂ or S₁ were selected through resonance conditions. We observe a broad vibrational band at 1770 cm^?1 in S₂ already. With 200 fs it decays and transforms into the well‐known S₁ Raman line for an asymmetric C=C stretching mode. Low‐frequency activity (<800 cm^?1) in S₂ and S₁ is also seen. A dependence of solvent lines on solute dynamics implies intermolecular coupling between β‐carotene and nearby n‐hexane molecules.     

Vibrational structure of the electron transition to the second excited singlet state of pyridine N-oxide

The vibrational structure of the electron transition to the second singlet excited state of pyridine N-oxide has been studied. The frequency of the 0–0 transition is 34502 cm⁻¹. A computer-aided technique for the assignment of the frequencies of the normal vibrations of polyatomic molecules in the excited electronic states is proposed. The frequencies of the totally symmetric vibrations of pyridine N-oxide in the second singlet electronically excited state are assigned. N. G. Chernyshevskii Saratov State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 36, No. 2, pp. 350–355, March–April, 1995. Translated by I. Izvekova     

Ir absorption spectrum of CrO2Cl2 molecules for high-lying states of the vibrational quasi-continuum

A new approach to the spectroscopy of highly excited vibrational states of polyatomic molecules has been elaborated. The molecules of CrO₂Cl₂ were prepared in states with a vibrational energy of the ground electronic term A₁ of ≈ 19000 cm⁻¹ by means of internal conversion of electronic energy from the electronic state B₁ excited by laser radiation. The spectroscopy of the vibrationally excited molecules has been carried out in the region of the ν₆ and ν₁ bands with diode and CO₂ lasers. The fwhm of the obtained spectrum was ≈ 15 cm⁻¹. The intermode interaction in CrO₂Cl₂ has been theoretically analyzed, and the calculated spectrum compared with that measured experimentally. The time evolution of the spectrum of vibrationally excited CrO₂Cl₂ molecules has been studied. The average energy transferred per one collision with unexcited CrO₂Cl₂ molecules was equal to 〈δE〉 ≈ 1200 cm⁻¹.     

Time-resolved electronic Raman spectrum of terbium aluminum garnet excited with visible and UV laser sources

Excitation profiles for the intensities of electronic Raman transitions between crystal field components of the ⁷F₆ and ⁷F₅ manifolds of terbium aluminum garnet are recorded for excitation in the spectral region where absorption bands due to levels of the ⁵D₄ manifold occur. The intensities of the electronic transitions are not enhanced which is thought to be caused by the small values of electric dipole matrix elements of the resonating electronic states in comparison to the values of such elements to other intermediate states which occur in the expression for the scattering tensor. Fluorescence from the ⁵D₄ levels is induced and resonance fluorescence are time resolved with respect to the Raman transitions. We report electronic Raman transitions excited with the 308.0 nm line of an XeCl excimer laser. As opposed to excitation with visible laser sources, transitions are recorded which terminate on all the crystal field levels of the ⁷F_5…0 levels. In addition, fluorescence from ⁵D₃ to the ground state of terbium aluminum garnet is also observed.     

Ab initio calculations of the ultraviolet resonance Raman spectra of uracil

An equation been derived to calculate, ab initio, the frequencies and intensities of a resonant Raman spectrum from the transform theory of resonance Raman scattering. This equation has been used to calculate the intensities of the ultraviolet resonance Raman spectra from the first π-π* excited state of uracil and 1,3-dideuterouracil. The protocol for this calculation is as follows: (1) The force constant matrix elements in Cartesian coordinate space, the vibrational frequencies, and the minimum energy ground and excited state geometries of the molecule are calculated ab initio using the molecular orbital program Gaussian 92, (2) the force constants in Cartesian coordinates are transformed into force constants in the space of a set of 3N – 6 nonredundant symmetrized internal coordinates, (3) the G matrix is constructed from the energy minimized ground state Cartesian coordinates and the GFL = LΛ eigenvalue equation is solved in internal coordinate space, (4) the elements of the L and L^?1 matrices are calculated, (5) the changes in all of the internal coordinates in going from the ground to the excited state are calculated, and (6) these results are used in combination with the transform theory of resonance Raman scattering to calculate the relative intensities of each of the 3N – 6 vibrations as a function of the exciting laser frequency. There are no adjustable parameters in this calculation, which reproduces the experimental frequencies and intensities with remarkable fidelity. This indicates that the Dushinsky rotation of the modes in the excited state of these molecules is not important and that the simplest form of the transform theory is adequate. © 1995 John Wiley & Sons, Inc.