Electronic spectrum of 1,5-naphthyridine: Vapor spectra

Analyses of the vapor spectra of 1,5-naphthyridine-d₀ and -d₆ are presented. The spectra are characterized by two principal origins, one the true electronic origin, magnetic dipole allowed, ${}^1\text{B}{}_{\mathrm{g}}\text{←}{}^1\text{A}{}_{\mathrm{g}}$, 27 598.5 cm^?1 (-d₆ 27 676.9), and the other a vibronic origin, electricd-dipole allowed, corresponding to the activity of a low-frequency vibration 6a_u, 183 cm^?1 (-d₆ 163). Extensive sequence structure is evident and the relative intensities of the sequence bands associated with the two origins provide the strongest argument for their assignments. The absence of 6a_u as a major source of intensity in the hot bands is in agreement with vibronic coupling calculations which propose that in absorption intensity “flows” to the lower-frequency vibrations.     

Vibrational spectrum and assignments for 1,6- and 1,8-naphthyridine

Assignments of all 42 fundamental vibrations of 1,6- and 1,8-naphthyridine are reported. Assignments were made from infrared and Raman spectra, comparison with naphthalene and related azanaphthalenes, and the results of a normal coordinate calculation of the fundamentals.     

Electronic spectra of parafluorobromobenzene

The electronic absorption spectrum of parafluorobromobenzene is reported together with its band shape and molecular geometry. The electronic transition is found to be the 2900–2400 Å system and the analysis consistent with other paraheterohalogenated benzenes. The intense bands, including 0–0, are double headed and areB-type in nature.A-type vibronic bands are also observed although less intense than theB-type bands. In all 9 excited states and 5 ground state fundamentals could be assigned.     

Electronic spectra of potassium bromide containing thallium II. Emission spectrum excited at 2537 Å

The emission spectrum of KBr: Tl⁺ excited at 2537 Å has been measured in the temperature range 15–296°K. At low temperatures the spectrum consists of a prominent band at 4.01 eV, a much smaller band at 3.40 eV and a very small band at 3.15 eV. The last does not appear to change much with temperature and so could not be measured accurately. The temperature-dependence of the two main bands is complex. Between 60 and 100°K the low-energy band increases sharply in intensity, while the high-energy band decreases correspondingly. Above 110°K the situation reverses and the low-energy band decreases in intensity while the high-energy band grows. Both bands closely approximate symmetric Gaussians. The temperature-dependence of the intensity of these two bands is well-explained qualitatively by the existence of two kinds of minima on the adiabatic potential energy surface for the A state. However, predictions of the temperature-dependence of the two emission bands based on calculated adiabatic potential energy surfaces are not in quantitative agreement with the experimental results. Possible reasons for this are our lack of knowledge of precise values for the parameters which enter into the theory, namely the spin-orbit coupling constant, the exchange integral, and the electron lattice coupling constant. The possible role of the ³A_1u state in emission is discussed briefly.     

Electronic spectra of azanaphthalenes: Solid state spectra of cinnoline and quinazoline

The first electronic absorption region ($\text{π}{}^1\text{← n}$) of cinnoline has been measured in durene and naphthalene as host crystals at 4 K and of quinazoline likewise in durene, naphthalene, and the pure crystal. The $\text{π}{}^1\text{← n}$ region is analyzed as a single transition in both cases in agreement with prior vapor studies, but all the spectra are complicated by the presence of at least two inequivalent sites with site splittings as large as 450 cm^?1. In one instance (quinazoline in naphthalene) polarization ratios permit the conclusion that the two observed site spectra correspond to the two alternative placements of the guest molecule in a vacancy in the host lattice. Site and host dependent effects are documented on phonon activity, vibrational frequencies, polarization ratios, and the incidence of vibronic (Herzberg-Teller) activity.The salient properties of the first $\text{π}{}^1\text{← π}$ absorptions of both molecules and of the $\text{π}{}^1\text{→ π}$ phosphorescence of quinazoline are briefly noted.     

The spectroscopy of salicylaldehydes: Electronic absorption spectra

Measurements of the electronic absorption spectra of vapor- and solution-phase salicylaldehydes are reported for wavelengths ≥1900 Å. Three intense absorption band systems are readily assigned as $\text{A′ (ππ}{}^1\text{) ← 1}{}^1\text{A′}$ transitions by comparison with all-valence-electron computations. Moderate vibrational structure in the $\text{3}{}^1\text{A′ (ππ}{}^1\text{) ← 1}{}^1\text{A′}$ transitions of isotopic salicylaldehydes is analyzed and tentative assignments are made for the coupled vibrations.     

Electronic spectra of mono-substituted chromates

The electronic spectra of monosubstituted chromate ion derivatives, CrO₃X^-, where X^-=F^-, Cl^-, Br^- and IO₃ ^-, have been measured at liquid helium temperature, employing a variety of sample forms. The observed electronic transitions correlate simply and directly with those of CrO₄ ^2-, the lowest-lying transitions being only very weakly perturbed. Of particular interest is that the lowest excited state ¹ E^a retains the peculiarities of the ¹ T ₁ parent state of CrO₄ ^2-. The sharp line spectrum observed in Cr₂O₇ ^2- between 18 000 and 19 000 cm^-1 is identified as ¹ E^a (¹ T ₁ in T _d) ←¹ A ₁ in a single O₃CrO⁼ chromophore. It is suggested that the observed features of the low-lying absorption bands can be explained by assuming that two spin-triplet states [³ E, ³ A ₂] are located a few hundred wave numbers above the sharp 0-0 line of ¹ E^a ←¹ A ₁.     

Electronic spectrum of praseodymium monoxide

Emission and absorption spectra of praseodymium monoxide were investigated. In the 5000–11,200 Å region the bands of 22 systems were found. The rotational structure of four bands belonging to two systems was analyzed. It has been shown that in absorption there are observed transitions at least from two electronic states having close values of vibrational and rotational constants.     

Electronic structure and spectra of CuO

We report the electronic structure of monoclinic CuO as obtained from first principles calculations utilizing density functional theory plus effective Coulomb interaction (DFT + U) method. In contrast to standard DFT calculations taking into account electronic correlations in DFT + U gave antiferromagnetic insulator with energy gap and magnetic moment values in good agreement with experimental data. The electronic states around the Fermi level are formed by partially filled Cu 3d _x²?y² orbitals with significant admixture of O 2p states. Theoretical spectra are calculated using DFT + U electronic structure method and their comparison with experimental photoemission and optical spectra show very good agreement.     

Electronic structure and spectra of N-methylfullerenepyrrolidine

A quantum-chemical analysis of the donor-acceptor properties of a C₆₀ + dimethylenemethylamine binary system is performed. It is shown that the term of the intermolecular interaction is two-well, because of which the optimization of the system structure at the initial distances between the molecules of 0.21 nm or smaller leads to the formation of N-methylfullerenepyrrolidine C₆₀. At initial distances exceeding 0.25 nm, a weakly bound charge transfer complex with almost complete retention of the properties of the individual molecules is formed. The low-temperature emission and absorption vibronic spectra of N-methylfullerenepyrrolidine C₆₀ in the crystalline toluene matrix are studied experimentally. It is found that the absorption spectra of the fulleroid and pure fullerene in the region corresponding to the excitation of the lowest electronic states are generally similar. The difference observed between the low-frequency spectra agrees completely with the quantum-chemical analysis performed.