  Spinons are among the generic excitations in one-dimensional spin systems,
they can be massless or massive. The quantitative description of massive
spinons poses a considerable challenge in spite of various variational
approaches. We show that a representation in terms of hopping and Bogoliubov
spinon processes, which we call "spinon-pair" operators, and their combination
is possible. We refer to such a representation as second quantized form.
Neglecting terms which change the number of spinons yields the variational
results. Treating the bilinear and quartic terms by continuous unitary
transformations leads to considerably improved results. Thus, we provide the
proof-of-principle that systems displaying massive spinons as elementary
excitations can be treated in second quantization based on spinon-pair
representation.
