Positions Of Transitions Research Articles

Zeeman–Raman Transitions of Tb^3+ in a Cubic Crystal*

From the behavior of the positions of electronic Raman transitions of the trivalent terbium ion of TbAlG as function of an external magnetic field (Zeeman–Raman effect), the energy of four of the lowest-lying electronic states of the split 7F6 manifold has been determined.

Study of the Ordered Magnetic State of Copper Formate Tetrahydrate by Antiferromagnetic Resonance

A brief account of antiferromagnetic-resonance (AFMR) measurements in single crystals of monoclinic Cu${(\mathrm{HCOO})}_{2}$.4${\mathrm{H}}_{2}$O has been reported, and it was shown that a model of weak ferromagnetism of the easy-plane type is not consistent with the data. This paper presents in detail the AFMR data and includes calculations of the AFMR modes and the magnetization based on assuming that Cu${(\mathrm{HCOO})}_{2}$4${\mathrm{H}}_{2}$O is very nearly an antiferromagnet in zero magnetic field. AFMR measurements have been made between 1.4 and 15\ifmmode^\circ\else\textdegree\fi{}K. Resonance transitions have been observed at 9 GHz, from 32 to 36 GHz, from 50 to 80 GHz, and from 107 to 124 GHz in magnetic fields up to 26 kOe. From the angular dependence of the field positions of the resonance transitions, a set of "principal axes" ${a}^{\ensuremath{'}\ensuremath{'}}b{c}^{\ensuremath{'}\ensuremath{'}}$ of the magnetic crystal have been determined. ${a}^{\ensuremath{'}\ensuremath{'}}$, the antiferromagnetic axis, is shown to be 8.5\ifmmode^\circ\else\textdegree\fi{} away from the $a$ axis toward the $c$ axis. The AFMR modes and the magnetization have been calculated on a two-sublattice model, based on a bilinear exchange interaction, assuming ${a}^{\ensuremath{'}\ensuremath{'}}$ as the antiferromagnetic axis, $b$ as the intermediate axis, and ${c}^{\ensuremath{'}\ensuremath{'}}$ as the hard axis. This calculation is an extension of one by Cinader by including the hard-plane anisotropy and an anisotropic antisymmetric $g$-tensor. It is found that a magnetic field (perpendicular to ${a}^{\ensuremath{'}\ensuremath{'}}$) larger than a critical field induces a weak ferromagnetic state. The calculation also shows that both antisymmetric exchange and the antisymmetric Zeeman interaction contribute to the effective canting fields. For the ${c}^{\ensuremath{'}\ensuremath{'}}$-axis case, the calculations are in good agreement (except for a constant gap in the low-frequency mode above 5.3 kOe) with the data and an effective canting field ${{H}_{\mathrm{DM}}}^{\ensuremath{'}}=84$ kOe is obtained. For the $b$ axis, the experiment indicates an instability in the antiferromagnetic axis at 5.3 kOe. The calculations also suggest an instability in the antiferromagnetic axis if a second effective canting field ${{h}_{\mathrm{DM}}}^{\ensuremath{'}}$ is negative; however, a quantitative fit to the AFMR modes has not been possible. A simplified calculation for the ${a}^{\ensuremath{'}\ensuremath{'}}$ axis is in fair agreement with some of the ${a}^{\ensuremath{'}\ensuremath{'}}$-axis data. The temperature dependence of the low-frequency zero-field mode is found to deviate substantially from the prediction of the molecular field approximation. A temperature-dependent contribution to the AFMR line-width of ${T}^{3.3\ifmmode\pm\else\textpm\fi{}0.2}$ is found.

Study of the Ordered Magnetic State of Copper Formate Tetrahydrate by AFMR

A brief account of the antiferromagnetic resonance (AFMR) measurements in single crystals of monoclinic Cu(HCOO)2·4H2O has been reported1 and it was shown that a model of weak ferromagnetism of the easy plane type is not consistent with the data. This investigation shows that most of the AFMR and magnetization data can be explained if one assumes that Cu(HCOO)2·4H2O is an antiferromagnet in zero magnetic field. AFMR measurements have been made between 1.4° and 15°K. Resonance transitions have been observed at 9 GHz, from 32 to 36 GHz, from 50 to 80 GHz, and from 107 to 124 GHz in magnetic fields up to 26 kOe. From the angular dependence of the field positions of the resonance transitions a set of ``principal axes'' a″bc″, of the magnetic crystal have been determined. a″, the antiferromagnetic axis, is shown to be 8.5° away from the a-axis toward the c-axis. The AFMR modes and the magnetization have been calculated on a two sublattice model, based on a bilinear exchange interaction, assuming a″ as the antiferromagnetic axis, b as the intermediate axis, and c″ as the hard axis. This calculation is an extension of one by Cinader2 by including the hard-plane anisotropy and an anisotropic, antisymmetric g-tensor. It is found that a magnetic field (perpendicular to a″) larger than a critical field induces a weak ferromagnetic state. The calculation also shows that both antisymmetric exchange and the antisymmetric Zeeman interaction contribute to the effective canting fields. For the c″-axis case the calculations are in good agreement (except for a constant gap in the low-frequency mode above 5.3 kOe) with the data and an effective canting field H′DM=84 kOe. is obtained. For the b-axis the experiment indicates an instability in the antiferromagnetic axis at 5.3 kOe. The calculations also suggest an instability in the antiferromagnetic axis if a second effective canting field, h′DM, is negative, however a quantitative fit to the AFMR modes has not been possible. A simplified calculation for the a″-axis is in fair agreement with some of the a″-axis data. The temperature dependence of the low-frequency zero-field mode is found to deviate substantially from the prediction of the molecular field approximation. A temperature-dependent contribution to the AFMR linewidth of T3.3±0.2 is found. A detailed paper on the experimental results and the calculations mentioned above will be published elsewhere.3

Transitions in creep behaviour

Attempts to identify the mechanisms operating during creep are often made by examining plots which yield apparent activation energies, or the stress or grain size-dependences of creep-rate. The forms of such plots are here examined and the ambiguities which arise near transitions from one regime to another are noted. The ranges of temperature, stress and grain size commonly used are inadequate and serious errors in interpreting the results of creep tests will continue to be made until a better understanding of the interaction of the basic processes is developed, so as to enable the positions of transitions to be predicted.

SPECTROCSOPIC STUDIES OF PURINES—III. PROPERTIES OF PURINES SUBSTITUTED AT THE SIXTH AND NINTH POSITIONS*

Abstract— We have investigated the effects of solvent and pH on the absorption and emission propertied of various 6‐ and 9‐substituted purines as a means of examining the nature of the directed not only at deteriming the relative energies of (π,π*) and (π,π*) states, but in particular, at examining the nature and energies of the two lowest‐lying (π,π*) states. For examplem, the attachment of a methyl or ribosyl group to the N9 of purine does not change the relative energies of the lowest‐lying (π,π*) and (π,π*) states; thus, the latter is the singlet of lowest energy. However, the lowest singles in derivatives formed by substitution at C6 are(π,π*) states—i.e. there is no long‐wavelength tail in the absorption spectra and florescence is comparable in intensity to phosphorescence. Further the absence of emission from neutaral adenine at room temperature is due to temperature quenching. Both lowest (π–π*) transtions. are contained under a common envelope and cannot be resolved in the absorption spectra. The shoulder observed in some of these compounds on the long‐wavelength slope of absorption envelope is vibrational in nature. Consideration of the effects of solvents on absorption and the analysis of luminescence spectra make it possible to locate the relative position of these (π–π*) transitions within the common envelope. In compounds with an ‐H on N9 and a free (aza) N1 (e.g. adenine, anionic hupoxanthine) the weaker, solvent‐sensitive (W) band has a higher energy then the more intense, solvent‐insensitive (S) band. When N1 is protonated, (e.g., in hypoxanthine or cationic adenine) and/or when methyl or ribosyl is substituted at N9, the order of these bands is inverted due ot a red shift of the W band. This shift is most apparent in the 9‐substituted hypoxanthines, where in non‐polar solvents the W band can be readily resolved in the absoption spectra. This inversion results in a red shift of both fluorescence and phophorescence and an increase of the P/F ratio. When chlorine or iodine is attached at C6 only phosphorescence having a very short lifetime appears due to heavy atom enhancement of single—triplet transitions.

Phonon-Induced Relaxation in Excited Optical States of Trivalent Praseodymium in LaF3

Temperature dependence of linewidths and positions of optical transitions of trivalent praseodymium doped lanthanum fluoride

Die Berechnung der Elektronenübergänge im Diphenyl nach der Methode des verzweigten Elektronengases

Hitherto, a complete interpretation of the absorption bands of biphenyl has not been given. Therefore, the positions of the electronic transitions as well as their polarizations and oscillator strengths are calculated from the branched electron gas model. For a planar molecule, two transitions result which are polarized parallel to the long axis and which by means of position and oscillator strength may be attributed to the observed transitions at 40 500 cm-1 and 50 000 cm-1, respectively. Further, two transverse transitions of lower intensity are obtained whose relation to the hidden transitions assumed in earlier papers 1,2,3 is discussed.

Two-Quantum Transitions in the Microwave Magnetic Resonance Spectrum of Atomic Chlorine

Two-quantum microwave magnetic resonance transitions corresponding to DELTA M/sub j/ = plus or minus 2 have been observed for both stable isotopes of atomic chlorine, Cl/sup 35/ and Cl/sup 37/. The experimentally observed and theoretically predicted positions of the two-quantum transitions agree within 13 parts per million, which was the precision of the experiment. The power dependence of the two-quantum transitions has been measured and checked with a variation of constants'' treatment of the microwave-induced probability amplitudes, and agreement has been found. Variations in intensity between corresponding DELTA M/sub j/= plus or minus 1 and DELTA M/sub j/ = plus or minus 2 resonances were observed and analyzed on the basis of time-dependent perturbation theory and the Schwinger-Karplus expression for the line shape of a collision-broadened resonance with saturation. Satisfactory agreement with theory is found for these intensity variations. The linewidths for the DELTA M/ sub j/ = plus or minus 2 lines are approximately half of that for the DELTA M/ sub j/ = plus or minus 1 lines; this is in agreement with the results of time- dependent perturbation theory. (auth)

A Comparative Study of Infrared Luminescence and Some Other Optical and Electrical Properties of ZnS : Cu Single Crystals

An attempt has been made to fix the position of the optical transitions leading to infrared luminescence of within the general picture of electronic states of crystal phosphors. For this purpose, many optical and electrical properties, such as emission spectra of the infrared and visible luminescence, excitation and quenching spectra of luminescence and photoconductivity as well as optical absorption spectra, have been investigated on the same single crystal within a temperature range between 4° and 300°K. Most of the experimental results could be explained in terms of a relatively simple energy band scheme, which differs in some respects from those published during the last years.

The decay of Au194

Abstract The decay of Au 194 was investigated by the use of high resolution spectrometers for the measurements of the conversion spectrum and a double lens spectrometer for coincidence measurements. By careful analysis of the conversion spectrum, which was recorded at a resolution of ≈0.2%, it was possible to identify more than 100 transitions in Pt 194 . The use of strong sources and a double counter operated in coincidence made possible the detection of lines of intensity only 10 −5 times that of the strongest line. Multipolarities could be found from K/L ratios for a few low energy transitions and some information could also be extracted from a comparison with results of previous gamma ray work. Energies of the strongest lines were measured absolutely by means of an iron free double focusing instrument, and further energy determinations were made relatively to these lines. The standard error of the measurements was frequently as low as 2 parts in 10 4 . A complete set of energy sums was computed in order to survey the possibilities of cascade-crossover combinations. The reliability of the numerical relationships was investigated statistically, and it was shown that a reasonably unique level scheme could be constructed on the basis of energies, although the positions of transitions remained to some extent ambiguous. The results of 79 coincidence experiments are reported, and when analyzed these data lead to a level scheme in agreement with the conclusions of the other approach. Furthermore, these experiments helped in deciding the location of transitions. Evidence for at least two 0 + states was found. The discovery of a level at 923 keV, probably of 4 + character, revealed a close analogy with the level scheme of Pt 192 . The interpretation of this level as a three-phonon state is in agreement with theory.

Spectrum of Inert Gases in their Second Stage of Ionisation

ARGON, krypton, and xenon when they are excited to their second stage of ionisation give rise to spectra which should theoretically come under quintet and triplet systems. The position of different transitions can without difficulty be predicted with the help of the ‘irregular doublet’ law and the ‘horizontal comparison’ law (Ind. J. Phy., vol. 3, part 1; 1928). Thus, with the knowledge of the nature and the position of the spectra we could identify certain lines and finally classified lines arising from the transitions below: