The “mini-exciton” in the pair of two translationally equivalent naphthalene C10H8 molecules in a C10D8 host as studied by electron spin echo and ODMR techniques

We have observed a temperature dependence of the phase memory time T_M in the lowest triplet state of the pair of two translationally equivalent naphthalene-h₈ guest molecules in a napthalene-d₈ host crystal in zero magnetic field. From this experiment we obtain the energy separation between the two Davydov components. Further we can make an estimate of the lifetime of the upper state which appears to be two orders of magnitude longer than the corresponding one in the translationally inequivalent pair.     

Fluorescence from γ-irradiated solutions of naphthalene and naphthalene-d8. Effect of an applied magnetic field

The fluorescence from continuously γ-irradiated solutions of naphthalene and naphthalene-d₈ is enhanced in a magnetic field. The enhancement is larger squalane than in cyclohexane but is smaller for naphthalene-d₈ than for the parent napthalene in both solvents. These observations are in general agreement with a recent theoretical model which describes the effect of a magnetic field on the rate of loss of spin correlation of geminate ion pairs prior to recombination.     

Isotopic mixed crystal exciton spectra in the far infrared: Naphthalene

The far infrared vibrational exciton spectra of isotopic mixed crystals of naphthalene-h₈ and d₈ were studied. The two observed translational phonon modes were determined to fall into the amalgamated band limit while the lowest energy B_3u, A_u and B_1u vibrational exciton bands were found to be in the separated band limit. The lowest energy B_3u “butterfly” mode with its large (15 cm^?1) exciton splitting was found to agree well with CPA calculations of mixed crystal spectra. A peak at 185 cm^?1 was also assigned as a peak in the vibrational exciton density-of-states of the B_3u mode.     

Franck—condon factors of the T1 ↷ S0 radiative and nonradiative transitions of naphthalene-h8 and -d8-a correlation function analysis

Franck—Condon factors for the T₁ ? S₀ transition in naphthalene-h₈ and naphthalene-d₈ are calculated employing the correlation function approach which allows us to investigate the distribution of the released electronic energy among the normal modes of the Final ground state. The relevant coupling parameters relating to geometry, frequency and anharmonicity changes due to excitation are included. Those related to geometry changes are obtained from the vibronic intensities of the phosphorescence spectrum as well as from a calculation implementing a semi-empirical relation between bond order and bond length. The calculated nonradiative rates compare well with the experimental rates in terms of absolute magnitude and deuterium effect. The semi-empirical calculations of the ribtonic intensities provide detailed information about force fields that are otherwise indistinguishable on the basis of their ability to reproduce infrared frequencies.     

EPR of triplet phenanthrene-d10 and naphthalene-dg in single-crystal biphenyl-h10 from 5–80K and its structural implications

A previously unreported phase transition in mixed biphenyl single-crystals, confined to at most a 5 degree temperature interval near 39 K, is described. Single EPR absorptions by triplet phenanthrene-d₁₀ and naphthalene-d_g above 39 K are converted by it into multiplets of four prominent components.     

The anisotropy of the optical polarizability of naphthalene-d8 in its lowest triplet state (photoselection method)

An equation is given for the evaluation of the anisotropy of the optical polarizability from the induced birefringence produced by photoselection. The anisotropy of the optical polarizability of naphthalene-d₈ in the lowest triplet state is calculated.     

Anisotropic spin—lattice relaxation in the triplet state of naphtralene-h8 in n-pentane

The temperature dependence of the individual spin—lattice relaxation rate constants (W_ij) between the lowest triplet sublevels of naphthalene-h₈ in a polycrystalline Shpol'skii matrix of n-pentane have been measured between 1.2 and 2.4 K in zero field. The total sublevel decay constants are evaluated and found to be independent of temperature. The W_ij are found to be highly anisotropic, but the anisotropy pattern differs from that observed previously in a durene matrix.     

Intersystem crossing in jet-cooled naphthalene, α- and β-chloronaphthalene as studied by sensitized phosphorescence excitation spectroscopy

The fluorescence excitation and sensitized phosphorescence excitation spectra of jet-cooled naphthalene-h₈, -d₈, α-chloro naphthalene, β-chloronaphthalene have been measured. It is shown that the intersystem crossing efficiency of naphthalene is large for specific vibronic levels in S₁. This efficiency is due to an accidental resonance with the vibronic level belonging to nearby T₂ state. Cl atom accelerates the intersystem crossing rate of naphthalene by about two orders of magnitude.     

Non-condon effects on radiationless triplet decay in benzene and naphthalene

Model calculations that avoid the Condon approximation are reported for T₁$\text{}\text{?}$ar S₀ intersystem crossing in normal and perdeuterated benzene and naphthalene. In both benzenes and in naphthalene-d₈, skeletal bending vibrations coupling T₁ to T₂ are found to be more efficient as accepting modes than CH-stretching vibrations.     

Deuteration effects on the phosphorescence of aromatic hydrocarbons

Observations of the phosphorescence decay of isotopic mixtures of naphthalene-h_s and -d_s, phenanthrene-h₁₀ and -d₁₀, and chrysene-h₁₂ and -d₁₂, in ethanol solutions at 77 K are analysed to determine the ratio k_PT^H/k_PT^D of the triplet radiative rate parameters of the perprotonated and perdeuterated compounds. The ratio is 1.20 (±0.07) for naphthalene, 1.39 (±0.06) for phenanthrene, and 0.98 (±0.04) for chrysene.     

Wavelength-dependent triplet state populating mechanisms of naphthalene in heavy-atom hosts

We have made zero-field optically-detected magnetic resonance measurements on the triplet state of naphthalene-d₈ incorporated in the heavy-atom host crystals p-dichlorobenzene, p-dibromobenzene, and s-tetrachlorobenzene. The dependence of the relative triplet sublevel populating rates on the exciting wavelength is interpreted in terms of the electronic excitation transfer mechanisms. We find that upon excitation of the host S₁ ← S₀ transition in p-dichlorobenzene, energy transfer to the guest T₁ takes place via the guest S₁, whereas in the other host crystals the intermediate is mainly the host T₁ band. Upon host T₁ ← S₀ excitaton, trapping takes place from a spin-aligned excitor band in s-tetrachlorobenzene, whereas the initial alignment is lost prior to trapping in the dihalobenzene hosts.     

Some comments on vibronic intensities of naphthalene fluorescence spectra from single vibronic levels

It is shown that some features of intensity distribution among certain vibronic transitions in naphthalene molecule can be understood, when one takes into account adiabatic and nonadiabatic interaction between S₁(¹B_3u), S₂(^tB_2u), and S₃(^IB_3u) electronic states. the vibronic activity of the $\text{6}\text{?}$(b_1g) mode in naphthalene-d₈ can be explained in terms of an anharmonic coupling with the $\text{7}\text{?}$(b_1g) mode. The theoretical analysis suggests reinterpretation of some vibronic transitions.     

Enantiodivergent formation of a chiral cytosine crystal by removal of crystal water from an achiral monohydrate crystal under reduced pressure

An achiral nucleobase cytosine forms an achiral monohydrate crystal (space group: P2₁/c) by crystallization from a water solution. It was found that the removal of crystal water under reduced pressure at room temperature afforded a chiral crystal of anhydrous cytosine (P2₁2₁2₁). The crystal chirality of anhydrous cytosine corresponds to the enantiotopic crystal face of the achiral monohydrate; therefore, when the enantiotopic b¹-face is exposed to the reduced pressure, dehydration occurred in the direction from the b¹-face to provide [CD(+)310_KBr]-cytosine crystal. In contrast, dehydration from the b²-face gave the opposite enantiomorphous [CD(?)310_KBr]-cytosine crystal. The correlation between enantiotopic faces and the formed crystal chirality is opposite to that from dehydration by heating. The formed chiral cytosine crystals act as a chiral trigger for asymmetric autocatalysis with enantioenrichment amplification of pyrimidylalkanol.     

Crystal growth kinetics of Sb2S3 in Ge–Sb–S amorphous thin films

Sb₂S₃ crystal growth kinetics in (GeS₂) _x (Sb₂S₃)_1?Cx thin films (x?=?0.4 and 0.5) have been investigated through this study by optical microscopy in the temperature range of 575?C623?K. Relative complex crystalline structures composed of submicrometer-thin Sb₂S₃ crystal fibers develop linearly with time. The data on temperature dependence of crystal growth rate exhibit an exponential behavior. Corresponding activation energies were found to be E _G?=?279?±?7?kJ?mol^?1 for x?=?0.4 and E _G?=?255?±?5?kJ?mol^?1 for x?=?0.5. These values are similar to activation energies of crystal growth in bulk glasses of the same compositions. The crystal growth is controlled by liquid?Ccrystal interface kinetics. It seems that the 2D surface-nucleated growth is operative in this particular case. The calculated crystal growth rate for this model is in good agreement with experimental data. The crystal growth kinetic characteristic is similar for both the bulk glass and thin film for x?=?0.4 composition. However, it differs considerably for x?=?0.5 composition. Thermodynamic and kinetic aspects of crystal growth are discussed in terms of Jackson??s theory of liquid?Ccrystal interface.     

The structure of orthorhombic Na2Ti9O19, a unit-cell twinning of monoclinic Na2Ti9O19, determined by 1-MV high-resolution electron microscopy

The crystal structure of the orthorhombic disodium nonatitanate, Na₂Ti₉O₁₉, has been determined on the basis of 1-MV high-resolution structure images, in which each site of the titanium and sodium atoms is clearly resolved. The crystal has an orthorhombic symmetry with lattice parameters a = 12.2, b = 3.78, and c = 30.1 Å. The space group of the crystal is either Ccmm or Cc2m. The crystal structure of the orthorhombic nonatitanate is closely related to that of the monoclinic nonatitanate reported previously in which the structure contains sodium titanium dioxide bronze-type units connected by bridging TiO₆ octahedra. The orthorhombic crystal can be described in terms of a unit-cell twinning of the monoclinic crystal. It is shown that migrations of sodium ions occur by electron beam irradiation.     

Crystal growth, structural, thermal, and dielectric characterization of Tutton salt (NH4)2Fe(SO4)2·6H2O crystals

A good quality single crystal of Tutton salt, (NH₄)₂Fe(SO₄)₂·6H₂O, with dimensions 6 × 7 × 3 mm³ was successfully grown by the slow evaporation growth technique at ambient temperature. The grown crystal was subjected to single crystal X-ray diffraction study which confirms that the grown crystal is monoclinic in nature with the space group P2₁/c. Optical absorption spectrum reveals that the grown crystal has good optical transparency in the entire visible region and its energy band gap was determined. The thermal behavior of the grown crystal was investigated by thermogravimetric and differential thermal analysis. The dielectric measurements were carried out to determine the dielectric behavior of the crystal.     

Thermostimulated structural changes in C60-CCl4 and C70-CCl4 crystal solvates

The crystal solvates in C₆₀-CCl₄ and C₇₀-CCl₄ systems obtained by crystallization from CCl₄ solution at room temperature were studied by IR Fourier spectroscopy and X-ray diffraction. The C₇₀ · (CCl₄) _n crystal solvate was obtained and studied for the first time; its hexagonal crystal lattice has unit cell parameters a = 10.658 ± 0.001 Å and c = 10.811 ± 0.002 Å. The temperature ranges of its destruction were determined.     

Three new tellurite halides with unusual Te coordinations and iron honeycomb lattice variants

The crystal structure of three new iron and copper-iron tellurite halides are presented; (I) Cu₃Fe₈Te₁₂O₃₂Cl₁₀ that crystallizes in the orthorhombic space group Pmmn, (II) Fe₈Te₁₂O₃₂Cl₃Br₃ that crystallizes in the monoclinic space group P2₁/c, and (III) Fe₅(TeO₃)₆Cl₂ that crystallizes in the triclinic space group P-1. The crystal structures were solved from single crystal X-ray diffraction data. All three compounds have layered crystal structures where the Fe atoms form variants of the honeycomb lattice. Highly unusual Te⁴⁺ coordination polyhedra are exemplified: [TeO₃₊₁E], [TeO₃XE], [TeO₃₊₁XE], and [TeO₃X₂E] (X=halide ion, E=the lone-pair valence electrons). The crystal structures contain large non-bonding volumes occupied by the stereochemically active lone-pair electrons on Te⁴⁺.     

Infrared and Raman spectra of crystalline para-bromoaniline at low temperatures

The polarization characteristics of the i.r. absorption bands of oriented p-bromoaniline crystal films have been studied at low temperatures. Raman spectra of this compound in solution and in the polycrystalline state have been recorded as an aid to the vibrational assignment of the crystal bands. The vibrational spectra are interpreted to deduce the crystal factor group (D_2h) and the molecular site symmetry (C_s). The observed factor group splittings and dichroic ratios suggest the crystal unit cell of p-bromoaniline to be isostructural with that of p-chloroaniline.     

Synthesis and study of a new kind of lead complex with variable coordination numbers

The crystal C₁₈H₁₂O₁₀Pb₃ is synthesized by Pb and phenyl propylene acid. The crystal is characterized by IR and single-crystal X-ray diffraction. The crystal belongs to monoclinic system, space group P2₁/c with the crystal cell parameters of a = 15.3263(14) Å, b = 16.3479(14) Å, c = 8.1006(7) Å, β = 92.3060(10)°, V = 2028.0(3) ų, and Z = 4. Through the molecular structure of complex, we can see that Pb has three kinds of coordination modes (5, 6, 7). The compound has formed a 1D surface shape structure through these coordinate modes with the ligand, and this 2D layer piles through C-H…π forms the 3D compound.