The chemical formula H1.9O1.9 is not a valid chemical formula. Chemical formulas represent the composition of molecules and compounds using symbols of elements and numerical subscripts to indicate the number of atoms of each element in the molecule.

In a valid chemical formula, the subscripts after the element symbols must be whole numbers (positive integers).

H and O symbols represent hydrogen and oxygen elements, respectively, in the given formula. However, the subscripts 1.9 and 1.9 are decimal numbers, which is not allowed in chemical formulas.

Therefore, H1.9O1.9 is not a valid chemical formula of a compound.