Millimetre wave spectrum of the weakly bound complex NH3-N2

The van der Waals complex NH₃-N₂ has been studied in the millimetre wave region, 76–106 GHz. Thirty-five lines were observed and assigned as pure rotational transitions, R(11) to R(15), belonging to six series involving all combinations of the parent molecule nuclear spin species, ortho/para-ammonia and ortho/para-nitrogen. Two of these series are continuations to higher J values of transitions observed previously in the microwave region, and the other four series were observed here for the first time. Predictions are given for a number of new NH₃-N₂ microwave transitions, and future observations of these should help to confirm the assignments given here. The time is ripe for theoretical investigations of NH₃-N₂ and the isoelectronic complex NH₃-CO.     

Fourth-order Finite-difference Methods for Two-point Boundary-value Problems

A number of new fourth-order accurate finite-difference methodsare developed for second-order ordinary differential equationsof the boundary-value type. Schemes are obtained for both linearand non-linear equations. In all cases, the solution of thedifference equations may be accomplished using a direct eliminationtechnique for linear tridiagonal matrix problems. The accuracyof the new methods is compared with existing finite-differencemethods on a theoretical basis as well as by considering a numberof example problems. It is concluded that the new methods offersignificant advantages for specific types of equations in termsof accuracy and/or computational efficiency.     

The weakly bound complex NH3-CO: Observation and analysis of spectra in the infrared (C-O stretching) and millimetre wave (76–106 GHz) regions

The van der Waals complex NH₃-CO has been studied in the infrared and millimetre wave regions, and analysed on the basis of the distinction between the ortho- and para- NH₃-CO nuclear spin species. The spectrum and energy level pattern of ortho-NH₃-CO are relatively simple, closely resembling those of the Ne-CO and Ar-CO complexes. The situation for para-NH₃-CO is somewhat more complicated, with observed states having K values which differ by ±1 from that of the analogous orthoNH₃-CO state. This indicates that the lowest energy orientation of para-NH₃-CO in the complex lies in a II configuration. The present results correlate very well with the only previous study of NH₃-CO, in the microwave region, and clarify the nature of the rotational series observed there. The infrared band centre of NH₃-CO is only very slightly shifted (<0.2cm^?1) from that of the free CO molecule, indicating that the CO vibration has little effect on the intermolecular forces.     

用穆斯堡尔效应研究YBa2Cu3O7-δ中的磁有序

以⁵⁷Fe作为探针,用穆斯堡尔效应研究YBa₂Cu₃O_7-δ的磁有序与超导电性的关系。实验结果可以用非声子超导机制进行定性解释。 关键词：     

Determination of the rotation-diffusion tensor orientation from NMR 13C-1H cross-relaxation rates

Taking advantage of the fact that α,α,2,6 tetrachlorotoluene possesses only one symmetry element (the aromatic ring plane), it proved possible to measure seven different ¹³C-¹H cross-relaxation rates which enable one to determine the three rotation-diffusion coefficients (D_xx , D_yy , D_zz ), in addition to the orientation of the relevant principal axis system (PAS) with respect to a chosen molecular axis system. It turns out that molecular reorientation is strongly anisotropic and that the rotation-diffusion PAS cannot be directly correlated with electrical molecular properties.