Explanation for 感 in 感叹词
There is virtually no difference. Perhaps 嘆詞 is more concise than 感嘆詞.
However, 嘆/叹 itself is seldom used alone in modern Chinese. Modern Chinese tends to use bisyllabic words. So we say 感嘆 (to interject), 讚嘆 (to praise), 嘆息 (to sigh) to 'augment' or 'specify' the meaning of 嘆/叹.
嘆詞 is already bisyllabic; but it still doesn't hurt to say it as 感嘆詞.
感 bears the concept of 'to feel'. You interject after you experienced an emotion. It confers neutrality and generality to the word 感嘆 (compare with 讚嘆, which is fairly positive).