Parametric fits of the atomic fine structure of ZrI and MoI

Least squares fits including effective two- and three-body interactions have been performed for the mixed configurations (4d+5s)⁴ in ZrI and (4d+5s)⁶ in MoI. A test of the eigenvectors in intermediate coupling derived from the fits has been accomplished by comparing calculatedg _J values andg _J values, which have been measured with high precision by atomic beam magnetic resonance. The agreement found is typically better than a few parts in 10⁴ except for some strongly mixed high-lying states in Mo.     

Avoided-crossing molecular-beam spectroscopy of CH3SiF3

The avoided-crossing molecular-beam method has been applied to CH₃SiF₃ in the ground torsional state. Stark and hyperfine rotational anticrossings have been studied, along with barrier anticrossings in which the zero-field energy differences depend only on the torsionial splittings. For υ = 0, pure rotational spectra were measured forJ = 13 ← 12 and 14 ← 13 with a mm-wave spectrometer and for J = 1 ← 0 with the molecular-beam spectrometer. Stark and Zeeman studies have been carried out with conventional beam techniques. From a simultaneous analysis of existing microwave data for υ ? 2 and the current measurements, it was found that the moment of inertia of the methyl top I_α = 3.170(2) amu A², the effective rotational constants A^eff = 4059.522(22) Mhz, and the effective height of the barrier V₃^eff = 413.979(14) cm^?1. The true values of A and V₃ have been obtained within certain approximations. The rotational constant B and several distortion constants including D_K were evaluated. In addition to determining the electric dipole moment μ 2.33938(14) D, the data yielded values for the distortion dipole constants μ_D and μ_J, and the molecular g-factors g_| and g_⊥.     

EPR of layered magnetic metal—amino acid salts. I. Cu(L-PHE)2

EPR measurements in single crystals of Cu(L-PHE)₂, the copper derivative of the amino acid L-phenylalanine, were performed at 300 K and 9.7 GHz. The gyromagnetic factor, g, and the linewidth of the single EPR line were measured in three perpendicular planes of the sample. The gyromagnetic tensor was obtained, and its principal values are g₁ = 2.211, g₂ = 2.134, and g₃ = 2.075. The single resonance is explained by the collapse of the resonances of the two magnetically non-equivalent copper sites due to the exchange interaction. The molecular g-factor of isolated copper ions is obtained from a model assuming axial symmetry. The results are g_| = 2.266 and g_⊥ = 2.075, indicating a d(x² - y²) ground orbital. The orientations of the molecules in the crystal obtained by this model are in agreement with the crystallographic values. The linewidth data support a model which assumes exchange narrowing of the magnetic dipolar interaction in a two-dimensional magnetic structure, an incomplete collapse of the hyperfine structure, and contributions arising from non-isotropic exchange. A mean value ¦J¦=0.19 K is calculated for the isotropic exchange interactions between one copper and its six copper neighbors in Cu(L-PHE)₂. Also, a lower limit ¦J′¦ > 0.02 K for the exchange coupling J′ between non-equivalent copper neighbors is obtained.     

Magnetic study of Cr ion in M2CrV3O11−x (MZn, Mg) compounds

Electron paramagnetic resonance (EPR) and magnetic susceptibility measurements on the recently synthesized vanadates M₂CrV₃O_11−x (M=Zn, Mg) have been analyzed. Two absorption lines with g≈2.0 (type I) and g≈1.98 (type II) were recorded in the EPR spectra, which can be attributed to V⁴⁺ ions and Cr³⁺ ion clusters (pairs), respectively. The exchange constant J between Cr³⁺ ions has been calculated, using both EPR and magnetic susceptibility data. Fitting of the EPR and magnetic susceptibility data has been carried out. The sign of J is a negative one for all samples and indicates antiferromagnetic interactions. Some difference in the J constant value among samples has been obtained. Volumetric titration confirms distinctly the presence of vanadium V⁴⁺ ions in the investigated compounds.     

Landé g J factor measurements in the 6snd 1,3 D 2 sequences of Yb I

The Landé g _J factors in the 6snd ^1,3 D ₂ sequences as well as states from the perturbing configurations of neutral Ytterbium have been measured by timeresolved fluorescence spectroscopy. Strong singlet-triplet mixing effects were observed. The g _J factors were measured using the Zeeman quantum-beat technique following step-wise laser excitation. The experiment provided new data for checking the Multi-channel Quantum Defect Theory (MQDT) used in energy-level and lifetime analysis.     

cw Two-photon transitions in K2 molecular beams

We report on the two-photon visible excitation spectra of potassium molecules in a supersonic beam. A dye laser excites K₂ to different (7s ¹Σ_g, 9s ¹Σ_g, 8d ¹Δ_g) Rydberg states. Two-photon transitions are detected by monitoring the resulting (third-photon) ionization. We have made detailed studies, including rotational assignment of 92 such transitions, ¹Δ_g(v¹, J¹) ← X ¹Σ_g(v = 0, J), where the B ¹Π_u state forms the intermediate enhancing state.     

Resonance-enhanced multiphoton ionization of molecular hydrogen via the E,F1Σg+ state: Photoelectron energy and angular distributions

Photoelectron energy and angular distributions are measured for the 2+1 multiphoton ionization process H₂ X¹Σ_g⁺ (ν = 0,J) + 2hv → E,F¹Σ_g⁺(ν_E,J_E = J) + hν → H₂⁺X²Σ_g⁺ (ν⁺) + e^?, for ν_E = 0, 1, or 2 and for J_E = 0 or 1 of the inner well of the double-minimum E,F state. Although a strong preference is found for ν⁺ = ν_E, the detailed H₂⁺ vibrational distribution does not exhibit Franck-Condon behavior, and the photoelectron angular distributions vary markedly with both the J_E value of the intermediate state and the ν⁺ value of the ion.     

The effect of the nitrogen non-bonding electron pair on the NMR and X-ray in 1,3-diazaheterocycles

The effect of the nitrogen nonbonding electron pair on the ¹J_C,H values of 1,3-diazaheterocycles was analyzed and compared to 1,5-diazabiciclo[3.2.1]octanes, which have a restricted conformation. The ¹J_C,H values were measured by observing the ¹³C satellites in the ¹H NMR spectra and then determining the ¹H-coupled ¹³C NMR spectra. The ¹J_C,H values are 10 Hz larger when the α-hydrogen is synperiplanar rather than antiperiplanar to the nonbonding electron pair on the nitrogen, which serves as experimental evidence of the orbital n_N→σ¹_C,Hap interactions. In addition, the homoanomeric effect from the interactions of the nitrogen lone pair with the antibonding orbital of the equatorial hydrogen, which was in the β position, was discussed (n_N→σ¹_C(β),Heq).     

Fine structure of the 1s5f and 1s5g levels of He I

The fine structure of the 1s5f and 1s5g levels of He I was measured using microwave spectroscopy. The helium atoms were excited by ion impact, and the eleven allowed 1s5f ^2S+1 F _J –1s5g ^2S′+1 G _J , transitions near ν≈15 GHz were induced and detected by measuring the 1s4d–1s2p or 1s3d–1s2p spectral-line intensities of the impact radiation as a function of the microwave frequency. The measured transition frequencies are in accord with theoretical values and, except for one transition frequency, with earlier experimental data. The existing discrepancy between these earlier data and theory could be solved.     

Tetranuclear copper(II) complex with the heterocyclic azomethine ligand: Crystal structure and magnetic properties

A tetranuclear copper(II) complex based on azomethine, which is the condensation product of 1-phenyl-3-methyl-4-formylpyrazol-5-one with 1,3-diaminopropan-2-ol, is synthesized. The complex includes two different tetranuclear clusters: symmetrical and unsymmetrical. They have a pseudo-cubane structure and are in a ratio of 1 : 2. The quantum-chemical calculation shows that the “unsymmetrical” conformer does not correspond to the local minimum on the molecular potential energy surface. Its existence is thus determined by the crystalline packing effects. According to the results of measurements of the temperature dependence of the magnetic susceptibility, the ground spin state is a singlet caused by the overall antiferromagnetic interaction between the copper ions. Accepting the molar magnetic susceptibility of the complex to be equal to the sum of susceptibilities of the “symmetrical” and “unsymmetrical” clusters and assuming that the spin-Hamiltonian for both clusters includes three exchange parameters, the temperature dependence of the magnetic susceptibility of the complex is satisfactorily described with the following parameters of the model: J _1A = ?178, J _2A = 80, J _3A = 18, J _1B = ?26, J _2B = ?74, J _3B = 46 cm^?1, g _A = g _B = 2.05.     

Molecular zeeman effect in NH3

High-resolution measurements of ΔM_j = 0 inversion transitions in ¹⁴NH₃ in 100 kG magnetic fields were made using a beam-maser spectrometer. The spectra show resolved splittings due to a different in molecular g-values for upper and lower inversion states with J = 3, K = 2. The observed difference in upper and lower inversion state g-values is g⁺(3,2)—g^?(3,2) = (1.38 ± 0.08) > 62;x 10^?4.     

Theoretical study of intra- and inter-chain magnetic interactions in [Ni(chxn)2Br]Br2

The intra- and the inter-chain magnetic interactions in [Ni(chxn)₂Br]Br₂, which is one of the typical one-dimensional (1-D) MX complexes are examined by using an unrestricted hybrid DFT (UB3LYP) method. Calculated effective exchange integral (J) value along the 1-D chain is 2J_Intra = −4016 K and is close to an experimental result (−3600 K). On the other hand, a very weak anti-ferromagnetic inter-chain interaction through Br⁻ ions is observed. The value is estimated to be 2J_Inter = −2 to −6 K. In addition to the J values, transfer integral (t), on-site Coulomb repulsion (U) and charge transfer energy (E^CT) values along the 1-D chain are also estimated to be 0.46, 2.46 and 0.6 eV, respectively.     

Rotationally resolved laser-induced fluorescence and zeeman quantum beat spectroscopy of the V 1B2 state of jet-cooled CS2

The rotationally resolved laser-induced fluorescence (LIF) excitation spectrum of V system bands (V¹B₂≈X¹Σ¹_g transition) of CS₂ cooled in a supersonic jet has been observed. In a supersonic jet of CS₂/Ar or He mixture, the rotational temperature of CS₂ is reduced to less than 10 K, and thus the LIF excitation spectrum is simplified significantly. Two types of rotational structure are found; one is composed of P and R branch transitions from even J″ levels and the other is of P, Q, and R branch transitions from even as well as J″. The bands with the former rotational structure are assigned to transitions to K′ = O levels of ¹B₂ state, the bands with the latter structure to transitions to K′ = 1 levels from the (O, 1¹, O) level of the electronic ground state, i.e. vibrationally hot bands. This assignment is supported by the further evidence that these hot bands disappear when the supersonic jet includes a third-body gas such as NH₃ which enhances the vibrational relaxation of CS₂. Calculation of transition moments for respective leads to the conclusion that the upper levels of the V system bands are located in the region close to or higher than the potential barrier of the bending vibration of excited CS₂. The radiative lifetime of CS₂ in single rovibronic levels of the ¹B₂ state is in the range of 2–8 μs which is of the same order of magnitude as that calculated from the absorption coefficient. It tends to be longer for higher J levels or for higher vibronic levels. Zeeman quantum beating is observed in the fluorescence decay of excited CS₂ for a number of rovibronic levels under a weak magnetic field, and thus a magnetic moment associated with each rovibronic level can be determined. The g values are around 0.02 and tend to be smaller in higher J levels for some vibronic states. Based on the the observed radiative lifetime and the g value, it is suggested that the ¹B₂ state is perturbed by a spin-rotation interaction with two spin components, A₁ and B₁ of the ³A₂ orbital state besides a strong spin-orbit coupling with the R ³B₂ state.     

Nonlinear level crossing spectroscopy of highly excited levels in yttrium using stepwise laser excitation

A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fields has been extended to the study of high-lying electronic levels excited by stepwise excitation with two cw dye lasers. The method has been applied to the determination of |A/g _J | values for four highly excited even-parity levels and two odd-parity levels in yttrium I. Using recently determined values of the magnetic hyperfine interaction constantA, Landég _J -factors have been deduced for these levels with an accuracy of about 1%. The results show significant differences from previous determinations.     

Contribution enthalpic in the interaction of activated carbon with polar and apolar solvents

A method is presented for calculating the contribution that enthalpies make for every component of mixtures of activated carbon–water and activated carbon–hexane to the immersion enthalpy using the concepts that are used in the solution enthalpies. The immersion enthalpies of microporous activated carbon in water and in hexane have values from ?18.97 to ?27.21 and ?25.23 to ?47.89 J g^?1, respectively. From the immersion enthalpies and mass relation of the activated carbon in each of the solvents, the differential enthalpies are calculated for the activated carbon in water, Hw_DIFac, with values between ?15.95 and ?26.81 J g^?1, as are the differential enthalpies for the activated carbon in hexane, ΔHh_DIFac, with values between ?6.86 and ?46.97 J g^?1. For a low mass relation of the mixture components the contributions to the immersion enthalpy of the activated carbon and water differ by 3.20 J g^?1, while the difference between the contributions of the activated carbon and hexane is 19.41 J g^?1.     

Conformation des dibenzoyl-2,4-pentanes. Relation avec les conformations locales des polyphenylvinylcétones atactique et isotactique

For the dl dibenzoyl-2,4-pentane, the difference δJ between the β methylene coupling constants and those of the α methine decreases slightly when the temperature is increased from ?25° to +160°. The conformational equilibrium tt ? g⁺g⁺ is not very mobile and exists only in CCl₄/CS₂ (90:10) solvent. In other solvents, the tt form is preponderant. The coupling constant variations are more important for the isotactic polymer than for the meso dibenzoyl-2,4-pentane model for which the observed variation is very weak (δJ = 0,7 Hz for ΔT = 220°). The g^?t and tg⁺ conformations have equal probability. These results are discussed in relation with those for the polymer.     

N2 rotational energy distributions in cold,supersonic beams from electron excited fluorescence measurements of N+2

Ground-state rotational energy distributions of N₂ molecules produced in pure and He-seeded supersonic expansions have been determined by measurements of the N⁺₂ first negative band rotational line intensities produced by 800 eV electron impact on cooled pure and He-seeded N₂ supersonic beams. Sufficient spectral resolution was employed to resolve completely both P and R branches of the first negative bands. Rotational state distributions were obtained to much higher values of J than in previous investigations. The data show that at 800 eV, the electric dipole selection rule, |ΔJ| = 1, is consistent with the observed N⁺₂ emission bands and that the rotational energy distributions produced in the cooled, supersonic beam are non-Boltzmann with a large population in the first few rotational states followed by a long, high-energy fail to quite high J values.     

Zeeman effect of superfluorescently populated 6snf 1F3 Ba I levels

Zeeman quantum beats of the Ba I 6snf ¹F₃ levels were measured between n=10 and 19 by time resolved recording of the exponential decay of the fluorescence on the 6snf ¹F₃ — 6s5d ¹D₂ transitions. The 6snf ¹F₃ levels were populated by superfluorescence pulses from the energetically higher lying 6s(n + 3)d ¹D₂ levels, the ¹D₂ levels were excited in a resonant two step process by two pulsed dye lasers. The experimental results of the g _J values in the 6snf ¹F₃ sequence are in fair agreement with the prediction of multi-channel quantum-defect theory.     

Temperature dependences of J(C,H) and J(C,D) in 13CH4 and some of its deuterated isotopomers

The nuclear spin—spin coupling constants J(C,H) and J(C,D) have been measured over the temperature range 200–370 K for the methane isotopomers ¹³CH₄, ¹³CH₃D, ¹³CHD₃ and ¹³CD₄. The coupling constants increase with increasing temperature for any one isotopomer and decrease with increasing secondary deuterium substitution at any one temperature. The results are entirely attributable to intramolecular effects and the data have been fitted by a weighted least-squares regression analysis to a spin—spin coupling surface thereby yielding a value for ¹J_e(C,H), the coupling constant at equilibrium geometry, and values for the bond length derivatives of the coupling. We find that ¹J_e(C,H) = 120.78 (±0.05) Hz which is about 4.5 Hz smaller than the observed value in ¹³CH₄ gas at room temperature. Results are also reported for J(H,D) in ¹³CH₃D and ¹³CHD₃ for which no temperature dependence was detected.     

Calculation of the 1J(PP) angular dependence in P2H4

Using the results obtained from an MO SCF ab initio calculation on P₂H₄ in four different conformations, the ¹J(PP) NMR coupling constants have been calculated. The ¹J(PP) values are highly dependent upon the rotational angle φ (?238.0 Hz in the eclipsed conformation, 10.9 Hz in the staggered one). The shape of the theoretical ¹J(PP) plot seems to be in good agreement with experimentally measured ¹J(PP) values.