In English there are many irregular verbs (Ex: 'I saw' is a irregular verbs, else You would use 'I seed'), anyway this isn't a irregular verbs. Infrared isn't a verb, Infrared is infra + red.
Emitted use a rules for regular verbs (verbs + ed) and we can divide emitted in emit (verb in present form) + ed. Using this rules it should be emited, but in English when there is a consonant you have to double it, It becomes emitted.
If you want look some other forms of verb to emit, you can look here