Amitāyus

I have re-evaluated my Sanskrit re-creation of the Amitāyus mantra from the Tibetan, which is on the Amitābha page. The Tibetan reads (in Unicode)

ཨོཾ༌ཨཱ༌མ༌ར༌ནི༌ཛི༌ཝན༌ཏེ༌ཡེ༌སྭཱ༌ཧཱ།

This is usually transliterated: om amarani dziwantaye soha which reflects Tibetan pronunciation. The actual syllables are: oṃ ā ma ra ṇi dzi wan te ye svā hā, from which I have now reconstructed the Sanskrit:

oṃ amaraṇi jīvantaye svāhā
ओं अमरणि जीवन्ताये स्वाहा

More details and Siddhaṃ calligraphy on the Amitābha page. Ideally I'd find a Sanskrit source for this mantra to clarify the matter - if you know one please let me know.