Electron impact excitation of high-lying states in the tungsten atom

Abstract

The extended crossed-beam method has been used to study excitation of high-lying levels in the tungsten atom. 40 excitation cross sections of WI spectral lines have been measured for exciting electron energy 50 eV. Two optical excitation functions were recorded in the electron energy range 0-200 eV. The results obtained were used to calculate the total excitation cross sections of 24 odd WI energy levels.Introduction. Tungsten plays an extremely large role in modern technology. This is because tungsten is the most refractory of the metals. Consequently, an obvious area of technical application of tungsten and its alloys are especially critical components and parts of structures operating under extremely high temperature conditions. Such conditions occur in vacuum technology, aviation, aeronautics, power engineering, etc.Moreover, study of different characteristics of tungsten is also of interest to basic scientific research. Tungsten belongs to the group of atoms in which filling of the 5d shell occurs. The first 5d electron appears in lanthanum, but then filling of the 5d shell stops and for the next 14 elements, the 4f shell is filled. A 5d electron is present only in cerium, gadolinium, and lutetium. The second 5d electron appears just in hafnium; then a monotonic increase in the number of 5d electrons continues all the way to iridium (5d 7 ), and for the next element (platinum) there are already 9 electrons in the 5d shell. For the next two elements (gold and mercury), the 5d shell is filled (5d 10 ). For all the atoms from 57 La to 77 Ir, the outer shell is a filled 6s 2 shell rather than a 5d or 4f shell being filled. In particular, for the tungsten atom the ground state level is the even level 5d 4 6s 2 a 5 D 0 .The optical spectra of tungsten and its neighbors in the Periodic Table of Elements are quite complex. The results of the initial studies of the WI spectrum have been systematized and analyzed in [1]. In that paper, 2378 spectral lines of the tungsten atom were assigned to 2567 transitions (including 169 double assignments and 10 triple assignments) using 50 even and 250 odd levels, of which 16 were established only tentatively. For 65 levels, sets of quantum numbers L and S were proposed within an LS coupling scheme, while the inner quantum number J was determined for most of the studied levels.The results of [1] with some additions and refinements were the basis for the well-known work in [2]. However, the results of the important papers [3,4], published three years earlier, were not taken into account in [2]. In [4], a theoretical assignment was made for the even levels of the tungsten atom in the energy range 0-42,000 cm -1 ; the energies of 89 levels were calculated, and a correspondence to experimental levels was established for 60 of them (tentatively for five of them). The remaining 29 levels have not yet been found experimentally. It has been shown that due to strong spin-orbit coupling and mixing of configurations, it is not enough to use LS coupling.So far, the most detailed information ...