Yes, HARMONICS is a Scrabble word!

Letter values in Scrabble US: H 4, A 1, R 1, M 3, O 1, N 1, I 1, C 3, S 1.

Is it a valid word?

HARMONICS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

the study of musical sound
a tone that is a component of a complex sound
any of a series of musical tones whose frequencies are integral multiples of the frequency of a fundamental