In رَبِّ, the rāʾ has fatḥah and is heavy. The bāʾ bears shaddah, but a doubled bāʾ does not receive the special ghunnah of a doubled nūn or mīm.
In الْعَالَمِينَ, the article lām is clear because ʿayn is a moon letter. Contrast the assimilated article in الرَّحِيمِ.
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Rabbi l-ʿālamīn: rāʾ and doubled bāʾ
Al-Fātiḥah: Integrated Tajwīd, Madd and Pausing Practice
In رَبِّ, the rāʾ has fatḥah and is heavy. The bāʾ bears shaddah, but a doubled bāʾ does not receive the special ghunnah of a doubled nūn or mīm.
In الْعَالَمِينَ, the article lām is clear because ʿayn is a moon letter. Contrast the assimilated article in الرَّحِيمِ.