Natural lacunae method and Schatten-von Neumann classes of the convergence exponent

The first our aim is to clarify the results obtained by Lidsky V. B. devoted to the decomposition on the root vector system of the non-selfadjoint operator. We use a technique of the entire function theory and introduce a so-called Schatten-von Neumann class of the convergent exponent. Considering strictly accretive operators satisfying special conditions formulated in terms of the norm, we construct a sequence of contours of the power type in the contrary to the results of Lidsky V. B., where a exponential type sequence of contours was used.