On subspectral acyclic molecular graphs

Based on the contraction and expansion of graphs, the subspectrality of acyclic molecular graphs is treated in a systematic way. The graphs containing eigenvalues 0, t 1 and ± 2 are discussed in detail, with emphasis on how to detect and construct the concealed species which can neither be recognized by symmetry considerations nor by the Heilbronner procedure. As a consequence, graphs and their counts have been given for species with numbers of vertices less than 16.Also known as Yuan-sun Kiang.