Zeeman Studies Research Articles

Magnetic Properties of Star-forming Dense Cores

Abstract Magnetic and energetic properties are presented for 17 dense cores within a few hundred parsecs of the Sun. Their plane-of-sky field strengths B pos are estimated from the dispersion of polarization directions, following Davis, Chandrasekhar, and Fermi (DCF). Their ratio of mass to magnetic critical mass is 0.5 ≲ M / M B ≲ 3 , indicating nearly critical field strengths. The field strength B pos is correlated with column density N as B pos ∝ N p , where p = 1.05 ± 0.08 , and with density n as B pos ∝ n q , where q = 0.66 ± 0.05 . These magnetic properties are consistent with those derived from Zeeman studies, with less scatter. Relations between virial mass M V , magnetic critical mass M B , and Alfvén amplitude σ B / B match the observed range of M/M B for cores observed to be nearly virial, 0.5 ≲ M / M V ≲ 2 , with moderate Alfvén amplitudes, 0.1 ≲ σ B / B ≲ 0.4 . The B − N and B − n correlations in the DCF and Zeeman samples can be explained when such bound, Alfvénic, and nearly critical cores have central concentration and spheroidal shape. For these properties, B ∝ N because M/M B is nearly constant compared to the range of N, and B ∝ n 2 / 3 because M 1/3 is nearly constant compared to the range of n 2/3. The observed core fields that follow B ∝ n 2 / 3 need not be much weaker than gravity, in contrast to core fields that follow B ∝ n 2 / 3 owing to spherical contraction at constant mass. Instead, the nearly critical values of M/M B suggest that the observed core fields are nearly as strong as possible, among values that allow gravitational contraction.

The longer timescale excited state dynamics of isolated benzene.

The excited state photodynamics of isolated benzene have been studied in the nanosecond range by two-step photoionization through various vibrations of the lowest singlet state, with imaging photoelectron spectroscopy detection. Photoelectron spectra are measured as a function of pump-probe delay time, and their time evolution is successfully compared to a biexponential decay function without regard to a particular kinetic model. The only reasonable kinetic model with only two exponentials is the one that involves an intersystem crossing from S1 to T1, although that model has previously been called into question by high-resolution studies that failed to find any singlet-triplet perturbations in Zeeman studies of the S1 spectrum. That contradiction remains unresolved.

New analyses of energy level datasets for LaCl3:Ln3+ (Ln = Pr, Nd, Er)

The electron spin–spin interaction (Hss) has long been omitted by many previous researchers in the empirical study of lanthanide spectroscopic data in the last four decades. In this work, the corresponding operator is specifically included into the semi-empirical Hamiltonian for 4fN tripositive lanthanide ions and its consequences are investigated by fitting the experimental energy level data available for LaCl3 doped with Pr3+, Nd3+ and Er3+, taking into account polarization and Zeeman studies. The inclusion does not require additional parameters. For these systems, respectively: 61, 127, 83 experimental crystal field levels were fitted by 14, 20, 20 parameters, giving root mean square (r.m.s.) errors (in cm−1) of 6.4, 8.1, 7.0. These errors are significantly smaller than those for best-fit calculations where Hss is omitted. With the exception of calculations by Crosswhite et al. for Pr3+ and Nd3+, the results of our present fits are significantly different from those of many previous researchers, probably attributed to errors or improper use of the reduced matrix elements for various free-ion operators. The inclusion of Hss into the energy level calculation can change state energies by almost three times the overall calculation r.m.s. error, and the changes vary considerably from one multiplet term to another. The spin–spin interaction has an effect upon the J-mixing between different multiplets and the impact can be appreciable in some cases, especially for dealing with the correlation crystal field. Since all the two body interaction operators are non-orthogonal within the 4fN configuration, their corresponding free-ion parameters are correlated with each other, depending upon the set of energy levels chosen in the fit. Hence, there is much doubt about the reliability of parameter values as derived from previous studies which are quite different from those of our present study.

Microwave and millimeter-wave spectrum of the He⋯H2+ long-range complex

The microwave and millimeter-wave spectrum of HeH2+ is reported over the frequency range 6–170 GHz. The observation of hyperfine structure in the spectra of some transitions made a clear distinction between the ortho- and para-hydrogen in the molecular ion. The hyperfine structure and double resonance Zeeman studies have enabled estimates of the quantum numbers involved in the transitions to be made. The Zeeman pattern in a 21.8 GHz doublet has been analyzed using an effective spin Hamiltonian with a case (B) basis set. This suggests an assignment of ΔN=+1, N=10←N=11. A similar analysis, in an extended hyperfine basis set, for the 15.2 GHz transition suggests an assignment of either ΔN=0, N=3, or N=4 as appropriate assumption from which to refine the potential.

Chromium in 4H and 6H SiC: Photoluminescence and Zeeman Studies

Chromium in 4H and 6H SiC: Photoluminescence and Zeeman Studies

Sideband optical–optical double resonance Zeeman spectroscopy. II. Studies of NiH, PdD, and PtH

Sideband optical–optical double resonance Zeeman spectroscopy is applied here to studies of the transition metal hydrides NiH, PdD, and PtH. For both NiH and PtH, in addition to obtaining Zeeman information on the ground and several excited electronic states, extremely small ground state proton hyperfine splittings have been resolved. For PdD, sub-Doppler spectra of the XΩ=0.5 ground state have been recorded even though the upper state in the optical transition is strongly predissociated. For all three radicals, the double-resonance Zeeman studies reveal that the g values in each state deviate from their nominal Hund’s coupling case (a) or (b) value with increasing rotational quantum number J. This Zeeman information, in addition to providing a sensitive confirmation of electronic assignments, also provides direct evidence of electronic state mixing (which is not present in ordinary non-Zeeman spectra) and useful in modeling the interactions between electronic states.

Zeeman study of Raman-active crystal-field transitions inNd2CuO4andSm2CuO4

We have measured by Raman scattering crystal-field (CF) transitions in Nd${}_{2}$CuO${}_{4}$ and Sm${}_{2}$CuO${}_{4}$ at low temperature in magnetic fields up to 16 T. The experimental results are in good agreement with theoretical calculations using a single-ion Hamiltonian which includes the CF potential, the rare-earth-Cu exchange interaction, and a Zeeman term. Furthermore, the measured Raman scattering intensities are in qualitative agreement with transition strengths predicted by calculations using second-order perturbation theory and the Judd-Ofelt approximation. Being sensitive to wave functions, such Zeeman studies provide a crucial test for the accuracy of CF Hamiltonians and their parameters.

Identification of an ionized-donor-bound-exciton transition in GaN

The transition involving an exciton bound to an ionized donor has been identified in GaN. The linewidth of the transition was not sufficiently narrow to permit identification from Zeeman studies. Instead, an alternative series of measurements including energy ordering of the ionized-donor-bound exciton with respect to the neutral-donor-bound exciton, line widths of the above two excitons, screening studies and electron bombardment measurements were used to identify the transition.

Zeeman studies of the first excited states of palladium and metal free phthalocyanines in Shpol’skii matrix

Phthalocyanines (Pcs) are planar molecules of relatively high symmetry and exhibit magneto-optic effects in many ways. We report the Zeeman effect of the first excited states of palladium (Pd–) and free-base (H2–) Pcs in a 5 K Shpol’skii matrix by direct observation of their fluorescence position shifts. From the experimental data an apparent angular momentum integral, coupling the lowest two Jahn–Teller stabilized crystal field split first excited states, Λ′, was found to be 2.7±0.1 ℏ for PdPc. No conclusive Λ′ was deduced for H2Pc but its value can be estimated to be around the theoretical value of 3 ℏ. The experimental data of H2Pc revealed a complex structure in the fluorescence band examined, which complicated the analysis of Λ′ but helped unravel the biexponential decay problem of the structure. We infer one narrower band in the structure has the previously reported lifetime of τ 6.3 ns, and the other broader band being ∼1.8 cm−1 higher, has τ 3.7 ns. We believe this composite situation also exists for the other tautomeric structure since it also exhibited biexponential decay.

Direct measurement of the rotational g-value in the ground vibrational state of acetylene by magnetic vibrational circular dichroism

The magnetic vibrational circular dichroism (MVCD) spectra of the v4 + v5 combination band of acetylene was measured. from the result for the P(J″ = 1 → J′ = 0) rotational transition, the gJ-value in the ground vibrational state for C2H2 was determined to be +0.049 (±0.005). The sign of the gJ-value measured by MVCD confirms that the correct sign is positive as found in a revised molecular beam magnetic resonance experiment and predicted on the basis of molecular Zeeman studies of other molecules and magnetic effects on heat flow in acetylene. MVCD offers an exceptionally simple method of determining the sign of molecular g-values for both the ground and excited states.

Identification of triplet levels by Zeeman studies of microwave–optical double resonance in the system of thioformaldehyde

Microwave-optical double resonance experiments have been carried out in the presence of magnetic fields on the 410 band of the [Formula: see text] system of thioformaldehyde. Several anticrossings have been observed. The series of levels 60 6, 70 7, …. 120 12 of the 41 Ã1A2 state is shown to be perturbed by the 63 3, 73 4, …. 123 9 levels of the 21 31 ã3A2 state. Two anticrossings involving high vibronic levels of the ground state (X* levels) are explained by interactions with the 85 level of the 2142 ã3A2 state.

Atomic Scale Properties of Normal and Inverted MBE-Grown Interfaces as Revealed by Zeeman Studies

ABSTRACTThe enhanced Zeeman effect of excitons in asymmetric CdZnTe-CdTe-CdMnTe quantum wells is studied quantitatively to gain information separately on the profile of the normal and inverted interfaces. The normal interface appears as more “abrupt” than the inverted interface. This behaviour is well accounted for if we assume that during the growth a rapid Cd/Mn exchange takes place between the surface layer and the subsurface one.

Optical Zeeman and low-field ODMR studies of thenπ* phosphorescence ofp-chlorobenzaldehyde

The emissive triplet states of p-chlorobenzaldehyde and p-chlorobenzaldehyde-d1 as guests in p-dimethoxybenzene host crystals are investigated by optical Zeeman and low field optically detected magnetic resonance (ODMR) studies of their phosphorescence at ⩽4·2 K. The active spin level, the sign of the principal fine structure splitting constant, its magnitude and the approximate location of the fine structure axes are deduced from high-field Zeeman perturbations of the phosphorescence origins of the guests. ODMR measurements confirm the conclusions and yield better values for the constants and locations of the principal axes of the fine structure tensor. The results for the perprotonated guest show that D ≡ -3Z/2 = -0·58290 and E ≡ (Y - X)/2 = -0·00714 cm-1; the fine structure axes are oriented relative to the host with the y axis nearly normal to the molecular plane and the z axis rotated 40° from the long molecular axis; and the phosphorescence arises predominantly from Tz . The d1-isotope of the guest ...

Electron paramagnetic resonance spectroscopy of tetrahedral Cr4+ in chromium-doped forsterite and åkermanite

The observation of near IR laser action in chromium activated forsterite by Petriĉević et al. [Appl. Phys. Lett. 52, 1040 (1988)] has spawned considerable interest in identifying and characterizing the quadrivalent chromium centers purportedly responsible for laser action in this material. The EPR (electron paramagnetic resonance) spectroscopy reported here of chromium-doped forsterite and structurally related åkermanite provides compelling evidence for the presence of tetrahedral Cr4+ centers in both materials. The EPR spectra reveal substitutional incorporation of chromium ions with triplet spin multiplicity, assignable to Cr4+. The fine structure and electron Zeeman interaction parameters of the centers in both materials are found to be very similar. In åkermanite, the Cr4+ center is unequivocally accommodated at tetrahedral lattice sites. The similarity of the spectroscopic properties of the Cr4+ ions in the two materials thus implicates incorporation at the analogous tetrahedral sites in forsterite. In conjunction with the findings of recent optical Zeeman studies [K. R. Hoffman et al., Phys. Rev. B 44, 12589 (1991); T. S. Rose et al., OSA Proceedings on Advanced Solid State Lasers 13, 17 (1992)], these EPR results demonstrate that tetrahedral Cr4+ is responsible for the near IR laser activity in chromium-doped forsterite.

Identification of triplet levels by Zeeman studies of microwave-optical double resonance in the à 1A 2-X̃ 1A 1 system of thioformaldehyde

Zeeman studies have been carried out on the 9831.1 MHz microwave-optical double resonance signal which connects the 7 07 rotational level of the 4 1 Ã 1A 2 excited state of thioformaldehyde with a high rovibronic level (X *) of the ground state. Anticrossin have been observed for several M J components of the double resonance signal at various values of the magnetic field strength. These results are interpreted in terms of a field-induced interaction of the 7 07 level with the 7 34 F 1 level in the 2 13 1 ã 3A which leads to the determination of the energy of the latter.

Optical studies of field-induced order in a singlet ground state dimer system

Optical Zeeman studies are reported for the ordered region of the singlet ground state dimer system Cs3Cr2Br9. The results are compared with earlier neutron scattering and AC susceptibility studies, and a model is suggested which not only describes the optical data, but also produces an excellent fit to the phase diagram as defined by the susceptibility results.

Structure of gold in silicon.

Detailed information on the electronic structure of the neutral substitutional gold center in silicon (Au 0 ) has been revealed from Zeeman studies of the donor and acceptor excitation spectra at 793 and 611 meV, respectively. The center is paramagnetic, S=1/2, with g ∥≃2.8 and g ⊥≃0, and has a static (100) tetragonal distortion

Avoided-crossing molecular-beam study of the torsion-rotation energy levels of CH 3CF 3

The avoided-crossing molecular-beam electric resonance method has been used to determine the leading parameters in the torsion-rotation Hamiltonian of CH 3CF 3, which was selected as a prototype for the case of a symmetric rotor with small (≤ 500 kHz) internal rotor splittings. Stark anticrossings have been studied for ( K= ±2↔∓ 1) with J= 2−6; hyperfine anticrossings have been studied for ( K= ±2↔0),(±2↔±1), and (±)↔0) with J≤2. A detailed investigation of the hyperfine case has been carried out involving selection rules, relative intensity calculations, Zeeman studies, and combination differences. Several pure rotational transitions for the lowest two torsional states have been measured between 93 and 114 GHz with a mm-wave spectrometer. The ( J= 1 ← 0) transition in the ground torsional state has been measured with the molecular beam spectrometer. Stark and Zeeman studies have been carried out with conventional molecular beam techniques. It has been determined that the effective rotational constant A eff=5502.904(3) MHz, the effective height of the threefold barrier to internal rotation V eff=1093 (11) cm −1 and the moment of inertia of the methyl top I α=3.21(4) Å 2. It has been found that the electric dipole moment μ=2.34720(13) D and the distortion dipole moment constant μ D=3.220(11) μD. The magnitudes and signs of the molecular g-factors have been obtained: g∥=−0.0226(13) nm and g ⊥=−0.117(1) nm. In addition, values have been determined for the B-rotational constant and several distortion constants.

Optical studies of the ( 4A2 × 2A1) and ( 4A2 × 2T2) singly-excited dimer states of Cs 3Cr 2Br 9

Optical absorption and Zeeman studies have been used to study both intra-configurational and inter-configurational transitions in the magnetic dimer system Cs 3Cr 2Br 9. The first analysis of the ( 4 A 2 × 2 T 2) and ( 4 A 2 × 2 A 1) singly-excited manifolds is presented in terms of an exchange theory applicable to multielectron occupancy of orbitally degenerate states.

Excitoic Recombination at a Transititon-Metal Related Defect in Silicon

AbstractA new photoluminescence system is reported for copper-doped silicon. The luminescence system consists of two doublet zero phonon lines at 1033.51±.05 meV, 1033.62±.05 meV, 1040.05±.05 meV and 1040.17±.05 meV. We establish from Zeeman studies that the lower energy lines are isotropic magnetic triplets, and the upper energy lines are singlets. From temperature dependence measurements the energy separation between triplet and singlet states is determined to be approximately 6 meV, in agreement with the spectroscopic separation. Also from temperature dependence PL we show that the transition probability ratio for the higher and lower states is 210. We conclude that the main features of the luminescence agree with radiative recombination of excitons bound to an axial isoelectronic defect. The chemical identity of the constituent(s) involved is uncertain although the participation of copper is likely.