G. Fleissner et al., NU(2) BAND REGION OF NITRATE AS AN INDICATOR FOR CONTACT ION-PAIRING IN AQUEOUS LITHIUM AND CALCIUM NITRATE SOLUTIONS, Journal of the Chemical Society. Faraday transactions, 92(1), 1996, pp. 23-28
Citations number
31
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
The FTIR spectra of 2 and 10 mol dm(-3) LiNO3 solutions, and of 0.5, 3
and 5 mol dm(-3) Ca(NO3)(2) solutions in D2O are shown in order to de
monstrate the usefulness of the nu(2) band region of nitrate as an ind
icator for contact-ion pairing in aqueous alkali-metal and alkaline-ea
rth-metal nitrate solutions. In fourth-derivative curves of the origin
al composite bands, the development of a second band and its increase
with concentration is seen at low frequency of the band, arising from
the 'free' nitrate. The band at low frequency is assigned to the conta
ct ion pair, and the assignment is supported by a parallel study of th
e nu(4) band region of the same solutions. The separation of the two b
ands in the nu(2) band region is between 3.3 and 5.2 cm(-1), and for 1
0 mol dm(-3) LiNO3 solution it is even less than half of the average h
alf-bandwidths of the two component bands. Reliable curve-fitting of t
he composite bands is possible, despite their strong overlap, by compa
rison of the fourth derivatives of the original composite bands with t
hose of the sum of the curve-fitted component bands. We suggest that t
his comparison of fourth derivatives can, for spectra of high signal-t
o-noise ratio, provide reliable curve fits even when the separation of
the peak maxima is less than half of the average of the half-bandwidt
hs of the component bands.