Molecular Dynamics Study of Aqueous Solutions IX. Dynamical Properties of an NH4Cl Solution

T h e d y n a m i c a l p r o p e r t i e s of a n a q u e o u s a m m o n i u m chlor ide solut ion h a v e been ca lcu la ted f r o m a molecu la r d y n a m i c s s i m u l a t i o n ove r 3.5 p icoseconds a t a t e m p e r a t u r e of 301 K whe re t h e basic per iodic c u b e c o n t a i n e d 200 w a t e r molecules, 8 a m m o n i u m ions a n d 8 chloride ions. T h e effect ive pa i r p o t e n t i a l s a r e b a s e d on t h e ST 2 w a t e r model , a rigid t e t r a h e d r a l fou r po in t cha rge model for N H 4 , a n d a s ingle p o i n t cha rge model for CI . T h e coefficients of self-diffusion a n d of ro t a t i ona l d i f fus ion , t h e spec t ra l dens i t ies of h inde red t r ans l a t i ons a n d of l ibra t ions , t h e cor re la t ion t i m e s of t h e dipole m o m e n t v e c t o r a n d t h e vec to r connec t ing t h e t w o p r o t o n s in a w a t e r molecule a re r e p o r t e d s e p a r a t e l y for t h e va r ious s u b s y s t e m s — N H 4 + , C I , bu lk wa te r , h y d r a t i o n w a t e r of NH4+ a n d C I — a n d a r e c o m p a r e d w i t h t h e ava i lab le e x p e r i m e n t a l d a t a . I m p l i c a t i o n s w i t h respec t t o t h e s t r u c t u r e b r e a k i n g ab i l i ty of t h e ions a re discussed.