Nitrogen Raman spectra

The Raman spectrum of the monohydrate, HN03.H20, shows it to exist as the hydroxoni-um salt, H30+N03 13. Also, according to analyses of the Raman spectrum, nitric acid exists in aq solns either as a pseudo-acid, N02.0H or as a true acid, N03".H+. In 10 molar aq soln, both acids are present in equal amounts, being caused by the self-dissociation of nitrogen pentoxide (NjOj), while in a 6 molar soln, the pseudo acid is present only to the extent of 2%. and the more dilute the soln, the less pseudo acid is present. In very coned solns, the true acid is present only in small quantities (Refs 32 33)... 

In the conclusion of the present chapter we show how comparison of NMR and Raman scattering data allows one to test formulae (3.23) and (3.24) and extract information about the relative effectiveness of dephasing and rotational relaxation. In particular, spectral broadening in nitrogen caused by dephasing is so small that it may be ignored in a relatively rarefied gas when spectrum collapse proceeds. This is just what we are going to do in the next sections devoted to the impact theory of the isotropic Raman spectrum transformation. 

Fig. 3.6. Density transformation of nitrogen isotropic Raman spectrum normalized to a maximum [89] (gas density is given in amagat).

Characterization of Surface Species by SERS. Before presenting the results obtained with 1, the spectral features which have proven to be useful in identifying surface species will be reviewed. Both in solution and by SERS, pyridines show a ring mode in the Raman spectrum near 1600 cm-. When the ring nitrogen is protonated, this band disappears and is replaced by a band near 1640 cm-1. The... 

Knaggs [10] found that in the case of cyanuric triazide the distance between the pairs of nitrogen atoms is not the same, being 1.26 and 1.11 A respectively. Examination of the Raman spectrum of sodium azide solutions has confirmed the chain structure of hydrazoic acid (Langseth, Nielsen and Sorensen [11]). The same conclusion is drawn from investigations of the absorption spectrum in the infra-red (Herzberg et al. [12]). 

Raman spectroscopy provide complementary information to IR in that bands that are inactive in IR often are active in Raman, and vice versa. The Raman spectrum of 1 consists of three bands with relatively high intensity [37, 38], while the corresponding spectrum for 3 has two strong and one weaker line [37]. Thus, in contrast to IR, Raman provides a tool for fingerprinting of both molecules even without the use of isotopic labeling. In addition, the detection limit is expected to be lower in Raman than IR due to the very low intensities of the IR transitions. We have recently estimated the detection limit for 1 in liquid and solid nitrogen based on experimental measurements and computed Raman intensities for 1 and N2. The following expression was used to compute the detection limit ... 

The low temperature refractive properties of the He gas have not been studied extensively. However, the second virial Kerr coefficient can be related to the zeroth moment of the polarized Raman spectrum, and thus deduced from the Raman experiment. For the helium gas at the liquid nitrogen temperature the experiment gives 1.46 a.u.416, the full quantum calculation 1.45328, while the classical result computed according to Eq. (1-260) gives 1.63 328. This shows that also for the Kerr effect the quantum corrections are important. A systematic study of these corrections and of the convergence of the semiclassical expansion has not been reported thus far, even though all necessary expressions are derived328. 

Thus the splitting is also much smaller for ND3 than for NH3. It is, furthermore, more correct to say that the pyramid of the hydrogen atoms with the nitrogen atom at the top is turned inside out than to speak of the motion of the nitrogen atom, the amplitude of which, in view of the larger mass, will only be very small. The splitting of the levels causes a doubling in the spectrum. While for the infrared absorption spectrum only the transitions from an antisymmetrical to a symmetrical level or vice versa are permissible, the lines in the Raman spectrum correspond to the transitions between levels of the same character. 

The molecule is pyramidal, having C3v symmetry with the nitrogen atom at the apex. The molecular dimensions have been determined by electron diffraction (266) and by microwave spectroscopy (161,271). The molecule with this symmetry will have four fundamental vibrations allowed, both in the infrared (IR) and the Raman spectra. The fundamental frequency assignments in the IR spectrum are 1031, vt 642, v2 (A ) 907, v3 (E) and 497 cm-1, v4 (E). The corresponding vibrations in the Raman spectrum appear at 1050, 667, 905, and 515 cm-1, respectively (8, 223, 293). The vacuum ultraviolet spectrum has also been studied (177). The 19F NMR spectrum of NF3 shows a triplet at 145 + 1 ppm relative to CC13F with JNF = 155 Hz (146, 216, 220,249, 280). 

The S4N ion (26) is a planar E,Z) chain with nitrogen as the central atom and short, terminal S-S bonds [ f(S-S) 190pm], which give rise to strong bands at ca. 565 and 590 cm in the Raman spectrum. The S4N ion is an 8 r-electron system and the intense visible absorption band near... 

It was possible to record a Raman spectrum of crystalline U(COT)2 under liquid nitrogen at 77 K. Bands due to ring-U-ring stretching and tilting were seen at 212, 236 cm-1 respectively.441 There have been several reports of matrix-IR studies of noble-gas (Ng) complexes of CUO, i.e. CUO(Ng)n. Table 8 summarises the data obtained for Ng = Ar, n = 1-4.442 444... 

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