The absorption spectra of polyatomic molecules containing methyl and ethyl radicals—III

The study of the absorption spectra of simple polyatomic molecules has many objects. As for diatomic molecules, it may lead to a deeper understanding of the interpretation of the spectra of polyatomic molecules in terms of spectral theory. As a consequence it may also lead to chemical data such as the energies of linkage, interatomic distances, and the electronic configurations of the molecules. In addition, it may help to explain the mechanism and nature of the primary processes in photochemical decomposition. In passing from diatomic to polyatomic molecules, however, two additional matters become of importance: on the one hand, the nature and types of vibration (valency or deformation, symmetrical or antisymmetrical) induced by the electronic excitation are of interest, and, on the other, it is desirable to examine how far symmetry properties assumed on the basis of independently determined molecular structures are borne out in the structure of their spectra. The difficulties in these studies are not solely due to the often very complicated structure of polyatomic molecule spectra, but also frequently to the continuous nature of these spectra in the ultra-violet region. It is with this region of absorption that photochemical considerations are usually concerned, the frequencies associated with it corresponding to transitions between the lower electronic states of the molecules. The interpretation of the continua is at the present time far from clear. In some cases work at low pressures reveals the existence of bands which so merge together with increasing pressure as to give effectively continuous absorption, whilst in other cases where the continua are apparently genuine, the influence of pressure upon the long wave limit of absorption is considerable. Even the conclusions to be drawn from the diffuse nature of the bands with polyatomic molecules are usually ambiguous, since it is not certain whether true cases of "predissociation" are involved or whether the large moments of inertia lead to unresolved close packing of rotational lines.

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The absorption spectra of some polyatomic molecules containing methyl and ethyl radicals

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1935.0124 ◽

1935 ◽

Vol 150 (871) ◽

pp. 603-614 ◽

Cited By ~ 13

Keyword(s):

Absorption Spectra ◽

Excited States ◽

Chemical Change ◽

Ultra Violet ◽

Polyatomic Molecules ◽

Point Of View ◽

Careful Examination ◽

Discrete Band ◽

Infra Red ◽

Ethyl Radicals

Although measurements on the ultra-violet absorption spectra of polyatomic molecules have rapidly multiplied in recent years, probably in no case has the structure of the entire spectrum been satisfactorily and completely interpreted. From the chemical point of view, investigations have been mainly directed to the study of “predissociation” processes and their correlation with the primary processes of photo chemical change, whilst in addition some knowledge has been gained in regard to the products of photodissociation and energies of linkage. A more careful examination of the matter has now shown that the inferences to be drawn from predissociation phenomena must be made with care, and in many cases additional measurements—for example of fluorescence or of quantum efficiencies—have to be made before the interpretations become unambiguous. From the physical standpoint, only a few band systems have been analysed in detail ( e . g ., ClO 2 , Urey and Johnston*; SO 2 , Watson and Parker,) and even in these the interpretations given may not be accurate. One aspect of the matter which has not yet received much attention, is the nature and type of the vibrations excited in polyatomic molecules. This may prove to be of considerable importance in connection with chemical kinetics. The chief difficulty in the analysis of the spectra of polyatomic molecules usually arises from their complexity, whilst the frequent occurrence of purely continuous spectra which may or may not overlap band systems often makes it impossible to derive much knowledge of the molecular excited states. In such cases as the latter, it may be that further in the ultra-violet, i . e ., in the Schumann region, discrete band systems may lead to knowledge of higher electronic states, but this region has so far been little explored. Herzberg and Teller* have recently attempted to construct selection rules for electronic and vibrational transitions in polyatomic molecules, but even when such rules as these are applied and when the infra-red and Raman frequencies are well known, the analysis of most band systems still remains very difficult.

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The Transformation of Thiols Compounded in Raw Rubber

Rubber Chemistry and Technology ◽

10.5254/1.3543119 ◽

1951 ◽

Vol 24 (4) ◽

pp. 914-915

Author(s):

Jeanle Bras ◽

Michel Montu

Keyword(s):

Absorption Spectra ◽

Analytical Method ◽

Ultra Violet ◽

Transformation Products ◽

Ultraviolet Absorption ◽

The Other ◽

Inert Gas ◽

Rubber Industry ◽

Acetone Extraction ◽

The One

Abstract During the last few years the rubber industry has made use of certain thiols, under the technical name of peptizing agents, which have the property of accelerating the plasticization of raw rubber during mastication. It is now known that this process of plasticization involves oxidation of the rubber, and that it does not take place in an atmosphere of an inert gas. Accordingly the present authors were induced, on the one hand, to follow the transformation of thiols during their participation in the mastication of rubber and, on the other hand, to observe their influence on the tendency of rubber to oxidize. In the first of these objectives, the analytical method utilized was ultra- violet absorption spectrography. To avoid pertubations in the spectra caused by the resins present in rubber, crepe rubber purified by acetone extraction was used in the experiments. The rubber was masticated at 100° C, and the thiol was added soon after the beginning of this mastication in the proportion of 5 per cent of the rubber. Samples were withdrawn at successive intervals of time, and the transformation products of the thiol, which were isolated by acetone extraction, were identified by their ultraviolet absorption spectra. In these experiments, chloroform solutions containing 0.5 gram per liter were employed.

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III.—The Absorption Spectra of Cyanogen and the Cyanogen Halides

Proceedings of the Royal Society of Edinburgh ◽

10.1017/s037016460001943x ◽

1933 ◽

Vol 52 ◽

pp. 152-158 ◽

Cited By ~ 4

Author(s):

R. B. Mooney ◽

H. G. Reid

Keyword(s):

Absorption Spectra ◽

Wave Length ◽

Ultra Violet ◽

Influence Of Temperature ◽

Long Wave ◽

Continuous Absorption ◽

Royal Observatory ◽

Influence Of Temperature On ◽

The Cost ◽

Cyanogen Halides

SummaryThe ultra-violet absorption spectra of C2N2, CNCl, CNBr and CNI have been photographed.Measurements are given of band edges of the C2N2 absorption spectrum in the region 2380 A–1850 A. The influence of temperature on the relative intensities of the bands has been studied.The long wave-length limits of the regions of continuous absorption due to the cyanogen halides are: CNCl, 2240 A; CNBr, 2540 A; CNI, 3100 A and 2150 A.We desire to thank Dr Baker, of the Royal Observatory, Edinburgh, for making photometer records of several spectra, Dr Ludlam for his helpful interest in our work, and Imperial Chemical Industries, Ltd., for a grant towards the cost of quartz apparatus.

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The absorption spectra of the halogen acids in the vacuum ultra-violet

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1938.0128 ◽

1938 ◽

Vol 167 (929) ◽

pp. 216-227 ◽

Cited By ~ 60

Keyword(s):

Absorption Spectra ◽

Wave Length ◽

Emission Spectra ◽

Ultra Violet ◽

Short Wave ◽

Molecular Ions ◽

Alkyl Halides ◽

Short Wave Length ◽

Continuous Absorption ◽

Continuous Background

Although the halogen acids have long been known to Possess regions of continuous absorption, no discrete electronic spectra have previously been reported for the neutral molecules. Their emission spectra occurring between 2800 and 4000 A really belong to the molecular ions. In the work to be described here, new absorption spectra of the halogen acids, which consist of very intense system of relatively discrete bands, have been dis-covered in the Schumann region. The spectra are essentially in the nature of strong resonance bands and are very similar in this respect to corresponding bands of the alkyl halides (price 1936). Extensive absorption systems of I 2 , Br 2 and Cl 2 have also been found in the same region. These will be described in a later publication. The continuous background against which the bands were observed was provided by the Lyman continuum. Other experimental details have been reported previously (Collins and Price 1934). The absorption spectrum of hydrogen iodide is shown in fig. 1 a (Plate 11). This particular photograph corresponds to a pressure of about 0·01 mm. in a path length of 50 cm. The most striking feature of the spectrum is the presence of a large number of bands with strong sharp Q branches accompanied on either side by weaker P and R branches (fig. 1 a, b, c ), the rotational structures of allied are only slightly degraded. This indicates that a relatively non-bonding electron is being excited, a fact which is also substantiated by the absence of any pronounced vibrational progressions. For example, the first strong band at 1762 A is unaccompanied by any vibrational bands, there doing a transparent region more than 5000 cm. -1 wide to the short wave-length side of it. Though the rotational structures of the P and R branches of this band are diffuse, the sharp nature of the Q branch is easily discernible (see fig. 1 a, c). The spectra of HBr and HCl each begin with a very similar band occurring at 1491 A for HBr (fig. 1 d ) and at 1331A for HCl (fig. 1 e ). It will be shown that these bands are related to one another and are analogous to the B bands of the alkyl halides. The next strong bands on the short wave-length side of them can further be linked with the C bands of the alkyl halides. Because of certain peculiarities which the above bands of the halogen acids (fig. 1 c, d, e ) exhibit, they will be discussed together in a later paragraph.

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On the absorption spectra of some higher oxides

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character ◽

10.1098/rspa.1933.0025 ◽

1933 ◽

Vol 139 (838) ◽

pp. 397-405 ◽

Cited By ~ 8

Keyword(s):

Oxygen Atom ◽

Absorption Spectra ◽

Light Absorption ◽

Wave Length ◽

Long Wave ◽

Continuous Absorption ◽

The Difference ◽

Heat Of Dissociation ◽

Wave Limit ◽

Excited Oxygen

Very little work has been done on the absorption spectra of the higher oxides, but recently, one of us has found that SO 3 gives a continuous absorption, beginning from a long wave limit, and after retransmission of a patch of light absorption again sets in. It was postulated that the first long wave limit of absorption by SO 3 marks the photochemical dissociation into SO 2 and normal oxygen atom, according to the equation SO 3 + hv 1 = SO 2 + O ( 3 P). (1) From this formula the heat of dissociation of oxygen was obtained with the help of some thermochemical data. The second long wave limit of absorption was attributed to the dissociation of SO 3 into SO 2 and excited oxygen, according to the process, SO 3 + hv 2 = SO 2 + O ( 1 D 2 ) (2) the difference between the two beginnings of absorption giving approximately the energy of excitation of oxygen from 3 P to 1 D 2 states. In this paper we have studied the absorption spectra of a few more higher oxides, viz., N 2 O 5 , TeO 3 , MoO 3 . As expected, all of them showed the same type of absorption as SO 3 . There was a first absorption on the long wave length side, followed by a patch of retransmitted light, which was again succeeded by a second region of absorption. The methods of procedure are described below.

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