The file format of meta-atoms has four, separated by a space, elements in the following order:
R/C///C/R LinearGeneralEthyne L-CtC LinearStructure
R/C///N LinearGeneralNitrile L-CN LinearStructure
R/H LinearHydrogenAtom L-H LinearStructure
R/'Br' LinearBromineAtom L-Br LinearStructure
R/'Cl' LinearChlorineAtom L-Cl LinearStructure
R/'I' LinearIodineAtom L-I LinearStructure