Determination of the dipole moment of thioformaldehyde in the a3A2 excited state by laser phosphorescence excitation spectroscopy

Doppler-limited phosphorescence excitation spectra have been recorded at various electric fields for two rotational transitions in the $\text{a}$³A₂-$\text{X}$¹A₁ 0-0 band of H₂CS. Stark splittings were resolved, and were used to determine the dipole moment in the excited electronic state. The value found, 0.57(3) D, is of the order expected by comparison with dipole moments determined for other states of H₂CS, but rather lower than that predicted by ab initio calculations.     

Analysis of the molecular bands of D2H and H2D at 5600 Å

Spectral simulation was used to analyze the molecular rovibrational bands of D₂H and H₂D at 5600 Å. These bands were previously measured by the ion beam neutralization method. They were assigned to the electronic 3p²B₁ ? 2s²A₁ and vibrational (ν - ν″) = (0, 0, 0,-0, 0, 0) transitions. Least squares fits to the experimental line-positions were made to determine the asymmetric rotator constants A, B and C for the 2s²A₁ and 3p²B₁ ν = 0 states of D₂H and H₂D, hitherto unknown. Lorentz line-profiles were assumed for the D₂H and H₂D rotational lines, whose widths are mainly governed by the lifetimes of the lower states. The bands at 5600 Å were simulated and the 2s²A₁ state lifetimes were estimated to be σ ≥ 0.5 ± 0.2 ps for D₂H and σ ≥ 0.4 ± 0.2 ps for H₂D. Vibrational constants of D₃ and D₂H in the 2s²A₁ states are determined from the positions of the 0-0 and 0-1 vibrational bands given in respective experimental spectra previously measured. For the first time the vibrational constants ω₁ and ω₂ of the 2s²A₁ state of H₂D were estimated from the positions of the 0-0 and 0-1 band maxima. These vibrational constants are compared with the corresponding vibrational constants of their ions.     

Ab initio study,including electron correlation,of the electronic structures,the dipole moments,the static polarizabilities and of the harmonic force fields of H2CO,H2CS and H2SiO

Ab initio calculations including electron correlation (on the PNO-CI and CEPA-PNO levels) are carried out for the isovalence electronic molecules H₂CO, H₂CS and H₂SiO, and for comparison also for H₂O and CO. The CEPA equilibrium distances are accurate to within 0.003 Å, while SCF results show significantly larger errors. The harmonic force constants on CEPA level are satisfactory as well, but for stretching of double or triple bonds inclusion of singly substituted configurations is imperative. Dipole moments were obtained with an error of 0.1 Debye from CEPA calculations with sufficiently large basis sets and inclusion of singly substituted configurations. The dipole polarizabilities are less sensitive to correlation effects but require larger basis sets.The population analysis reveals that the SiO bond in H₂SiO is highly polar and thatd-AO's cannot be regarded as valence AO's in any of the molecules of this study. The binding energy of H₂SiO (with respect to H₂Si(¹ A ₁) + O(³ P)) is predicted as 140 ± 5 kcal/mol. The contributions of different pairs in terms of localized orbitals to the correlation energy of the molecules of this study are analyzed.     

Vibrational radiative lifetimes in H2Se and HCS−

Vibrational dipole matrix elements and radiative transition probabilities for H₂Se and HCS⁻ have been evaluated from theoretical three-dimensional electric dipole moment and potential energy functions. The radiative lifetimes of the (v=1,J=0) levels of HCS⁻ have been calculated to be 3.5 ms (CH stretch), 172 ms (HCS bend) and 785 ms (CS stretch), and in H₂Se to be 122 ms (symmetric stretch), 1045 ms (bend) and 101 ms (asymmetric stretch). The lifetimes of higher vibrational states with no extensive mode-mixing decrease with increasing vibrational quantum number and vary in a mode-specific way.     

Lifetimes of the vibronic Ã2A1 states of H2O+ and of the 3Πi (υ′ = 0) state of OH+

Using the delayed coincidence technique, lifetimes have been measured for some Σ and Π vibronic òA₁ states of H₂O⁺ and for the ³Π_i (υ′ = 0) state of OH⁺ by analysing the decay curves of the òA₁(0, υ′₂, 0) ? X?²B₁ (0, υ″₂, 0) and the ³Π_i(υ′ = 0) ? ³Σ^?(υ″ = 0) emission intensities respectively. The excited molecular ionic states are produced via excitation of H₂O molecules by 200 eV electrons. For H₂O⁺(òA₁) the vibronic Σ levels with υ′₂ = 13 and 15 and the vibronic Π levels with υ′₂ = 12 and 14 have been considered. The radiative lifetimes obtained for these levels have about the same value, namely 10.5(±1) × 10^?6 s. The radiative lifetime for the OH⁺(³Π_iυ′= 0) state is 2.5(±0.3) × 10^?6 s. The lifetimes found in this work for H₂O⁺(òA₁) and OH⁺(³Π_i,υ′= 0) are about ten and three times longer respectively than the corresponding lifetimes given by other investigators [1,2]. The probable reason for this discrepancy is that in the other experiments no attention has been paid to the presence of a large space charge effect. This effect is caused by the positive ions which are created by the primary electron beam.     

Microwave—optical double resonance in the A1A2 excited state of thioformaldehyde

Microwave—optical double resonance experiments have been carried out on the 4_o¹ band of the $\text{A}$¹A₂$\text{X}$¹A₁ system of thioformaldehyde (H₂CS). More than 100 microwave and radiofrequency transitions have been observed in the $\text{A}$¹A₂ excited state. Many of these transitions are magnetically sensitive. Some of the excited state levels are perturbed by triplet levels and others by high vibrational levels of the ground state.     

Ultraviolet photodissociation of bromopropane: Energy partitioning and curve potential crossing analysis

The photodissociation mechanism of bromopropane (C₃H₇Br) molecule in the UV region is treated within time-dependent numerical methods. The results and our ab initio calculations indicated that the absorption of C₃H₇Br in the investigated region primarily originated from the excitations to the lowest three repulsive states, as assigned as 2A ₂, 4A ₁, and 3A ₁ in C _s symmetry. Dissociations occurred on the PES surfaces of the three states, giving C₃H₇ + Br (² P _3/2) or C₃H₇ + Br* (² P _1/2) as two final products, and being impacted by an avoided crossing between the PES surfaces of the 3A ₁ and 4A ₁ states. The transition dipole to the 2A ₂ state was perpendicular to the symmetry plane, so perpendicular to the C-Br bond. The transitions to the 3A ₁ state was polarized parallel to the symmetry plane, and also parallel to the C-Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways and angular distributions of photofragments, for the photolysis of C₃H₇Br in the UV region.     

Lifetimes of the vibronic Ã2A1 states of H2S+

Lifetimes have been measured for the Σ and Π vibronic òA₁ states of H₂S⁺ by studying the decay curves of the òA₁ (0, υ′₂, 0) → X? ²B₁ (0, υ″₂, 0) emission bands. The vibronic òA₁ states are produced via excitation of H₂S molecules by 150 eV electrons. The Σ sublevels 1 ? υ′₂ ? 7 and the Π sublevels 3 ? υ′₂ ? 6 have been considered. Predissociation occurs in the Σ sublevels for υ′₂ ? 7 and in the Π sublevels for υ′₂ ? 6. The obtained radiative lifetimes for the non-predissociated Σ and Π sublevels are around 4.2(±0.4) × 10^?6 s and 5.6(±0.5) × 10^?6 s respectively. For the predissociated Σ(0, 7, 0) and Π(0, 6, 0) levels the corresponding lifetimes are 2.3(±0.3) × 10^?6 s and 1.6(±0.3) × 10^?6 s respectively. The rate constant for collisional deactivation (quenching) of the vibronic òA₁ states by H₂S molecules was found to equal 2.3(±0.3) × 10^?9 cm³ mol^?1 s^?1.     

Data on the thermochemistry of azoalkanes

The rate constant of the primary decomposition step was determined for four symmetrical and four unsymmetrical azoalkanes. From the experimental activation energies and some literature enthalpy data, the following enthalpies of formation of radicals and group contributions were calculated: ΔH_? (CH₃N₂) = 51.5 ± 1.8 kcal mol^?1, ΔH_? (C₂H₅N₂) = 44.8 ± 2.5 kcal mol^?1, ΔH_? (2?C₃H₇N₂) = 37.9 ± 2.2 kcal mol^?1, [N_A-(C)] = 27.6 ± 3.7 kcal mol^?1, [N_A-(?_A) (C)] = 61.2 ± 3.1 kcal mol^?1.     

Laser-induced fluorescence measurement of the vibrational distribution of CS formed in the reaction O + CS2 → CS + So

A frequency-doubled cw dye laser has been used to determine the initial vibrational distribution of CS formed in the reaction O + CS₂ → CS + SO by application of laser-induced fluorescence. The A¹5—X¹σ⁺ system of CS was excited, and rotationally resolved spectra of a number of bands measured. The vibrational distribution found for υ = 0–2 is 1.0:0.27:0.11, yielding a value of 6% for the fraction of reaction exoergicity entering vibration of this product. No evidence of high product rotational excitation wss detected for a reaction pressure 5 × 10^?3 Torr.     

TiO2基态和激发态的几何结构、激发能和偶极矩

采用二阶微扰理论MP2、密度泛函B3LYP方法和含时密度泛函TD-B3LYP方法分别优化了TiO₂分子的基态¹A₁和六个激发态¹B₂、³B₂、¹B₁、³B₁、¹A₂和³A₂的几何结构. ¹A₁、¹B₂、³B₂、¹B₁和³B₁具有弯曲几何结构, ¹A₂和³A₂具有线性对称结构. 我们发现激发态¹B₂、³B₂、¹B₁和³B₁键偶极矩的数值大小顺序和相应的键角大小顺序完全一致. 另外, 采用完全活化空间自洽场(CASSCF)CASSCF(6,6)、CASSCF(8,8)、多参考组态相互作用(MRCI)和含时密度泛函TD-B3LYP 计算了TiO₂ 分子各激发态的垂直激发能和绝热激发能. 对¹B₂、³B₂和¹B₁三个态, MRCI/CASSCF(6,6) 计算的垂直激发能和绝热激发能与已有的实验值最接近. 对其他三个激发态³B₁、¹A₂和³A₂, 计算的激发能和文献报道的激发能计算值基本一致. 最后, 还计算了TiO₂分子的基态和激发态的偶极矩. 对¹A₁和¹B₂态, 偶极矩的计算值与已有的实验值相吻合. 采用原子偶极矩校正的Hirshfeld 布居方法计算了TiO₂分子在¹A₁、¹B₂、³B₂、¹B₁和³B₁态时各原子的电荷, 发现从基态到激发态偶极矩的变化与电荷从氧原子向钛原子的转移有关. 整个计算中还考察了基函数cc-pVDZ、cc-pVTZ和cc-pVQZ对计算结果的影响.     

A system-independent correlation between the enthalpy and the entropy of dilution for polymer solutions

The second osmotic virial coefficient (A₂) and its entropic and enthalpic parts (A_2,s and A_2,H) have been determined, by means of light-scattering measurements, for solutions of polystyrene, polymethylmethacrylate and cellulose nitrate of different molecular weights in 19 solvents. A distinct qualitative correlation exists between A₂ and A_2,H and between A_2,s and A_2,H. The elimination of the “geometric” parameters of the polymer, by dividing these coefficients by suitably chosen reduction parameters, shows that the reduced coefficients obtained A₂⁰ and A_2,s⁰ are predominantly functions of the reduced enthalpy coefficient A_2,H⁰.     

Magnetic and charge transport properties of the Na-based Os oxide pyrochlore

The Na-based osmium oxide pyrochlore was synthesized for the first time by an ion-exchange method using KOs₂O₆ as a host. The composition was identified as Na_1.4Os₂O₆·H₂O by electron probe micro-analysis, thermogravimetric analysis, and structural analysis using synchrotron X-ray diffraction. Na_1.4Os₂O₆·H₂O crystallizes in a regular pyrochlore structure with some defects (space group: Fd-3m, a=10.16851(1) Å). Electrical resistivity, heat capacity, and magnetization measurements clearly showed absence of superconductivity down to 2 K, being in large contrast to what was found for the β-type pyrochlore superconductor AOs₂O₆ (A=Cs, Rb, and K). The Sommerfeld coefficient is 22 mJ K⁻² mol⁻¹, being the smallest among AOs₂O₆. A magnetic anomaly at ∼57 K and associated magneto-resistance (+3.7% at 2 K in 70 kOe) were found.     

The microwave spectrum,structure and dipole moment of thiocarbonyl fluoride,F2CS

The microwave spectrum of thiocarbonyl fluoride, F₂CS, has been investigated in the region 26.5–40.0 GHz. Transitions of the ¹⁹F₂¹²C₃₂S and ¹⁹F₂¹²C³⁴S isotopic species have been observed and the derived rotational constants yield the following ground stale structural parameters

The ground state rotational constants of the normal species are (in MHz)

The asymmetry parameter, x = ?0.62640, and the inertial defect Δ⁰ = 0.203 u A² which is consistent with that expected for this type of molecule, if planar.The dipole moment was determined from the Stark effect of two lines, and was found to be μ_A = 0.080 D.     

Novel drug‐based Fe(III) heterochelates: synthetic,spectroscopic, thermal and in‐vitro antibacterial significance

A series of novel heterochelates of the type [Fe(Aⁿ)(L)(H₂O)₂]^?mH₂O [where H₂Aⁿ = 4,4′‐(arylmethylene)bis(3‐methyl‐1‐phenyl‐4,5‐dihydro‐1H‐pyrazol‐5‐ol); aryl = 4‐nitrophenyl, m = 1 (H₂A¹); 4‐chlorophenyl, m = 2 (H₂A²); phenyl, m = 2 (H₂A³); 4‐hydroxyphenyl, m = 2 (H₂A⁴); 4‐methoxyphenyl, m = 2 (H₂A⁵); 4‐hydroxy‐3‐methoxyphenyl, m = 1.5 (H₂A⁶); 2‐nitrophenyl, m = 1.5 (H₂A⁷); 3‐nitrophenyl, m = 0.5 (H₂A⁸); p‐tolyl, m = 1 (H₂A⁹) and HL = 1‐cyclopropyl‐6‐fluoro‐4‐oxo‐7‐(piperazin‐1‐yl)‐1,4‐dihydroquinoline‐3‐carboxylic acid] were investigated. They were characterized by elemental analysis (FT‐IR, ¹H‐ & ¹³C‐NMR, and electronic) spectra, magnetic measurements and thermal studies. The FAB‐mass spectrum of [Fe(A³)(L)(H₂O)₂]^?2H₂O was determined. Magnetic moment and reflectance spectral studies revealed that an octahedral geometry could be assigned to all the prepared heterochelates. Ligands (H₂Aⁿ) and their heterochelates were screened for their in‐vitro antibacterial activity against Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Serratia marcescens bacterial strains. The kinetic parameters such as order of reaction (n), the energy of activation (E_a), the pre‐exponential factor (A), the activation entropy (ΔS^#), the activation enthalpy (ΔH^#) and the free energy of activation (ΔG^#) are reported. Copyright © 2009 John Wiley & Sons, Ltd.     

Study of singlet-triplet transitions in the ozone molecule using the multiconfigurational self-consistent field theory

The intensities and dipole moments of the lower singlet-triplet transitions ³ A ₂ ← X ¹ A ₁ and ³ B ₁ ← X ¹ A ₁ in the ozone molecule were calculated by the multiconfiguration self-consistent field theory with the quadratic response function. The results of calculations of the intensities of singlet-triplet transitions using different basis sets and complete active spaces were compared. The assignment of the ³ A ₂ ← X ¹ A ₁ transition in the ozone spectrum to the Wulf band is discussed.     

High-Resolution Threshold Photoelectron Spectroscopy by Vacuum Ultraviolet Laser Velocity-Map-Imaging Method

We have obtained the high-resolution threshold photoelectron (TPE) spectra of chlorobenzene C₆H₅Cl (X¹A₁), propargyl radical C₃H₃ (X²B₁), and allyl radical C₃H₅ (X²A₁) by employing the vacuum ultraviolet (VUV) laser velocity-map-imaging-TPE (VUV-VMI-TPE) method. The photoelectron energy resolution of 1-2 cm^-1 observed for the VUV-VMI-TPE method is comparable to that achieved in VUV laser pulsed-field ionization-photoelectron (VUV-PFI-PE) measurements. Similar to VUV-PFI-PE measurements, the energy resolutions for VUV-VMI-photoelectron (VUV-VMI-PE) and VUV-VMI-TPE measurements are found to depend on the dc electric field F in V/cm used at the photoionization region for electron extraction. The decrease of the ionization thresholds of C₆H₅Cl and C₃H₃ observed as a function of F shows that the Stark shift correction for VUV-VMI-TPE measurements is governed by the formula -3.1√F in cm^-1, which is half of the classical prediction of -6.1√F in cm^-1.} We have also measured the VUV-VMI-PE spectra of C₆H₅Cl and C₃H₅ at VUV energies near their ionization thresholds. The cationic vibrational bands observed in the VUV-VMI-PE measurements were assigned to be the vibrational progression, nv₇⁺ (n=0-3), for C₃H₅⁺. The higher experimental sensitivity and similar energy resolutions achieved in VUV-VMI-TPE compared to VUV-PFI-PE measurements make the VUV-VMI-TPE method an excellent alternative for high-resolution VUV-PFI-PE measurements.     

Anionic radical and protonated form of molecular ozone. A nonempirical calculation taking into account the electronic correlation

The different electronic states of ozone (¹A₁,³B₂,³A₂,³B₁, and 2¹A₁) were calculated by a nonempirical method in the basis 4–31 G (d, p) taking into account the electronic correlation according to the Meller-Plesset theory of a fourth order perturbation theory (MP4). The geometric structures of the ions O ₃ ^– and O₃H⁺ were calculated. The evaluation of the affinity to the proton for O₃ gave a value (P_A=6.8 eV) 1 eV lower than that for H₂O.Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. Rubezhansk Branch, Dnepropetrovsk Institute of Chemical Technology. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 28–32, March–April, 1993.     

Investigation in the Series of Substituted Butan- and Butenolides: XV. Transformations of 4-Hydroxy-2-butenolide in Water Media at Various pH Values

The 4-hydroxy-2-butenolide was established by polarographic method to undergo in water solutions fast tautomeric and acid-base transformations. Depending on pH of the medium the compound is present either as a cyclic irreducible form (at pH 0-4) or in the open-chain (carbonyl-containing) reducible forms (at pH > 4 and < 0). It is presumed that in going from the basic to strongly acidic medium and backwards occur consecutive equilibrium transitions of four species: cis--formylacrylic acid anion (A^-), its neutral molecule (HA) existing as linear and cyclic tautomers, and protonated forms (H₂A⁺ and H₃A⁺). The formation mechanism thereof is considered.     

两亲8-氨基喹啉衍生物的空穴传输特性及LB膜电致发光器件

在过去的20年里,电致发光(EL)领域的研究显得异常活跃,EL已应用于通讯、信息、显示等许多领域,而占领这一领域的是P-N结无机半导体发光二级管,其发光效率已超过了白炽灯.但由于无机半导体很难实现大面积平面显示,加之成本较高,因此,限制了其进一步的发展[1].有机荧光材料的种类繁多,荧光量子效率高,且可以通过分子结构修饰有目的地控制其发光效率、发光颜色和电学性能[2],因而,越来越多的学术界和工业界的研究小组进入了有机电致发光研究领域[3.4].