Vowel usage?

2 replies
Anonymous:
Hi

Please advise me regarding the vowel usage in the following sentence:

"The photoluminescence quantum yield of a W-based polymer was 15 times higher than that of an Rh-based one."

Thanks
Are you asking why 'an' and not 'a'?

An is used before a vowel sound not necessarily an actually written vowel. R is said as 'ar' or 'ah' - starting with an a sound.
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