Line intensities in 10B nuclear quadrupole double resonance spectra

Abstract

The line intensities in 10B nuclear quadrupole double resonance spectra (DRLC), which cannot correctly be predicted from the squares of the quantum-mechanical transition matrix elements, were calculated from the spin thermodynamics of the 42 level crossings during the field cycling. The results show that the intensity relations among the 21 lines of a 10B nucleus are only little affected by the 22 line crossings when the asymmetry parameter runs from 0 to 1. Hence a unified series of approximately valid figures for the relative line intensities in 10B double resonance spectra can be derived which are in order of decreasing frequency of the transitions near η = 0: 60, 40, 38, 22, 25, 14, 14, 6, 5, 1, 33, 16, 17, 5, 10, 2, 8, 3, 2, 3, 2. The presence of solid state transitions leads to an increased overall intensity of the spectral lines but does not change the line intensity ratios. The comparison of calculated line intensities with an experimental example (borazine, B 3N 3H 6; e 2gQ( 10B) h : 6771 kHz, η:0.133) confirms the validity of the simple level crossing theory for 10B spectra and shows that the quantum-mechanically forbidden transitions have to be taken into account as well as the allowed ones, certainly because of the correspondent quadrupolar levels being mixing with closely neighbored other states.