Most composers of vocal music take great care to use music to emphasize the meaning of the libretto (or text to sing). And while composing the harmonics, it’s good to know that each vowel has various overtones. Helmholtz measured it as following:

Die Lehre von den Tonempfindungen als physiologische Grundlage für die Theorie der Musik von H. Helmholtz. play.google.com/store/books/details?id=nOosAAAAYAAJ Klänge der Vocale page 173