The crystal structure of a new form of L-isoleucine hydrochloride monohydrate C₆H₁₃O₂NHClH₂O (termed form II) has been determined using three-dimensional photographic data. This differs conformationally from the hydrochloride derivative (termed form I, Trommel and Bijvoet 1954) reported earlier. The crystal belongs to the orthorhombic space group P2₁2₁2₁ with cell dimensions,a=5.87±0.01,b=24.77±0.02 andc=6.85±0.01 Å and four molecules per cell,ρ_obs=1.240 g/cm³,ρ_cal=1.238 g/cm³,µ for CuKa=32.6 cm⁻¹.

Using the Bijvoet difference data reported in the literature for four compounds,viz./it, zinc sulphide, L-α-glyceryl phosphoryl ethanolamine monohydrate, 1-β-arabinofurinosyl cytosine hydrochloride and lithium aluminium oxide, the anomalous dispersion components Δf″ of the stronger anomalous scatterer in each case is calculated accepting the theoretical values for the lighter anomalous scatterers. For MoKα radiation the values turn out to be Δf″z_n=1.470 (85), and for CuKα Δf″_P=0.430 (25) Δf″_C1=0.715 (18) and Δf″_A1=0.264 (21).

The determination of the internal strains on the coupling parameter approach becomes very involved particularly when the number of atoms per unit cell is very large. It is shown in this paper that a knowledge of the site symmetry of the atoms helps one in determining the number of non-vanishing internal strain coefficients easily. The internal strain coefficients of two symmetry connected atoms can also be related. Examples are shown to illustrate these ideas.

The low-lying levels in⁷⁴As have been studied by means ofγ-ray and internal conversion electron spectroscopy following the⁷⁴Ge(p,n)⁷⁴As reaction. New levels at 372.7, 532.8, 632.1, 731.6, 752.7, 758.3, 801.6, 902.9 and 1128.5 keV, not observed in earlier studies, have been established.J^π assignments have been made to several low-lying levels. An earlier ambiguity regarding the identification of an isomeric level has been clarified. The half-life of a level at 271.4 keV has been measured to be 1.0±0.1 nsec; in addition, limits on half-lives of levels at 182.7, 277.5 and 425.4 keV have been assigned. The level structure is discussed on the basis of available nuclear models.

Shell model calculations for the nuclei⁹¹Mo,⁹²Tc and⁹³Ru in the Talmi approach have been done. The ground state binding energies and the excitation spectra agree with experiment.

Angle integrated cross-sections for the pion single charge-exchange reaction on¹³C and⁷Li have been calculated at several energies in the distorted wave impulse approximation employing the off-shell nature of the pion-nucleon scattering amplitude and using the Breit-Wigner formula for its energy dependence. Effect of the two nucleon correlations in the nucleus on the cross-section is also studied. Our results are in rough accord with the experimental data.

Five red degraded bands belonging to theC²Σ⁺ —X²Π system of NH⁺ were excited in a mild condensed discharge through flowing ammonia and were photographed on a 3.4 meter Ebert grating spectrograph at a dispersion of 2.5 A/mm. The rotational analyses of these bands enabled us to evaluate the vibrational and rotational constants accurately. The rotational energy levels of theΠ⁺ andΠ⁻ levels of theν=0 and 1 levels of the ground state,X²Π, were fitted in James expression using two sets of rotational constants. The perturbations observed in theX²Π state caused by thea⁴Σ⁻ state were examined in greater detail.

CNDO calculation is made for thioformamide, N-methylthioformamide (both in cis and trans forms) and N, N-dimethyl thioformamide. The charges, bond orders, dipolemoments and ionization potentials of molecules are discussed and comparison made with corresponding amides. The barrier to internal rotation about C-N bond for thioformamide and N-chloroacetamide is reported along with changes in the charges on atoms and dipolemoment of molecules with rotation. The trans form of N-methyl thioformamide is found to be more stable than cis isomer by 4.9 Kcal/mole.

The molecular volume of some polymers and linear molecules has been calculated as a function of the internal rotation angles around the non rigid bonds. The new method gives the same conclusions as derived from the calculation of the conformational potential energy. Therefore it seems that, in many cases, it is possible in a simple way to predict the more stable molecular conformations.