• N A Narasimham

Articles written in Proceedings – Section A

• Theβ- andγ-band systems of14NS and15NS

The spectra of14NS and15NS molecules are obtained in a 2450 mc./s. microwave oscillator discharge. Vibrational assignments of theβ- andγ-systems are studied in more detail. Several hitherto unrecorded bands are satisfactorily explained as belonging to higherv′,v″ levels in the Deslandres schemes of bothβ- andγ-systems. The observed isotope shifts (14NS-15NS) provide confirmatory evidence for the proposed vibrational analysis.

In the case of theγ-system, thev′=2 level of the upper state appears to be strongly perturbed showing a shift of about 38 cm.−1 from the expected position. In theβ-system, the isotopic shifts in the band-heads involving thev′=0 and 1 levels of the2Δ5/2 of the upper state show small deviations from expected values. The reality of these small deviations is established beyond doubt by the occurrence of the effect on the 0–0 sub-band which exhibits the isotopic head in a wavelength direction opposite to the expected one.

• A new2Π-X2Π band system of NS

Vibrational and rotational analysis of some bands forming a new band system of NS is given. It is also shown that the system involves the ground X2Πreg. state of the molecule, and is due to the transition2Πreg.→X2Πreg. The bands form a singlev″=0 progression withv′=7, 8, 9 and 10. The assignment of these quantum numbersv′, v″ is supported by (1) Δ2F″ (J) values which are identical with those for thev″=0 bands of theβ andγ systems and (2) the isotopic shift data from15NS bands, respectively. The derived vibrational and rotational constants for the new2Πreg. state are as follows (cm.−1 units):

• On the fine structure of the ultraviolet bands of S2

The ultra-violet bands of S2 reported first by Rosen and Desirant are studied under high resolution. The bands are excited in a microwave (2450 mc./s.) discharge through sulphur vapour containing34S in natural abundance and enriched to 44·4%. Rotational analysis of six bands at 2620, 2660, 2760, 2793, 2813 and 2847 Å shows that they involve a common1Δu1Δg system. The observed vibrational and rotational constants are

• Errata

• Rotational analysis of 2620 Å and 2760 Å bands of32S34S

Rotational analysis of bands of32S34S at 2620 Å and 2760 Å has been made, which confirms the earlier vibrational assignment of these bands. The band origins and isotope shifts of these bands are.

• 2Σ→X2Π, band system in PO molecule

The new ultra-violet bands of PO lying in the region 2300–3000 Å and degraded to the red, have been excited in a microwave (2450 mc./s.) discharge and photographed in the second and third orders of 3·4 m. and 6·6 m. grating spectrographs. Vibrational analysis of the R1 and Q2 heads shows that they can be expressed by the relation$$v_h = \left. \matrix{ 43852 \cdot 43 \hfill \cr 628 \cdot 60 \hfill \cr} \right\}\matrix{ { + 826 \cdot 37 (v' + \raise.5ex\hbox{\scriptstyle 1}\kern-.1em/ \kern-.15em\lower.25ex\hbox{\scriptstyle 2} ) - 6 \cdot 96 (v' + \raise.5ex\hbox{\scriptstyle 1}\kern-.1em/ \kern-.15em\lower.25ex\hbox{\scriptstyle 2} )^2 } \cr { - \left\{ {1233 \cdot 38 (v'' + \raise.5ex\hbox{\scriptstyle 1}\kern-.1em/ \kern-.15em\lower.25ex\hbox{\scriptstyle 2} ) - 6 \cdot 56 (v'' + \raise.5ex\hbox{\scriptstyle 1}\kern-.1em/ \kern-.15em\lower.25ex\hbox{\scriptstyle 2} )^2 } \right\}.} \cr }$$. Rotational analysis of the 0–2 and 0–3 bands shows that they arise out of a2Σ−X2Π transition.

The vibrational and rotational constants are

(a)2Σ (initial)state\eqalign{ & w_e ^\prime = 826 \cdot 37 cm.^{ - 1} w_e ^\prime x_e ^\prime = 6 \cdot 96 cm.^{ - 1} \cr & B_0 ^\prime = 0 \cdot 637_8 cm.^{ - 1} r_0 ^\prime = 1 \cdot 582_7 {\rm{{\AA}}} \cr}

(b)X2Π (final)state\eqalign{ & w_e ^{\prime \prime } = 1233 \cdot 38 cm.^{ - 1} w_e ^{\prime \prime } x_e ^{\prime \prime } = 6 \cdot 56 cm.^{ - 1} \cr & B_2 ^{\prime \prime } = 0 \cdot 719_8 a = 0 \cdot 005_2 cm.^{ - 1} \cr}

Coupling constant A2=224·22 cm.−1

• Thed1Σ+c1Π system of NH

The singlet systems of NH have been excited in a mildly condensed transformer discharge through flowing ammonia gas. The 0-0 bands, 2530 Å ofd1Σ+c1Π and 3240 Å ofc1Πa1Δ systems, appear with considerable intensity compared to the 4502 Å band of thec1Πb1Σ+ system. Besides the 2530 Å bands, two weaker bands at 2683 Å and 2516 Å are also excited. They are photographed in the second order of a Jarrell Ash 3·4 m. grating spectrograph at a dispersion of 2·6 Å/mm. Rotational analysis of the two weaker bands show that they belong to thed1Σ+c1Π system and further supports their assignment as the 0–1 and 1-1 bands. The vibrational and rotational constants derived for thed1Σ+ andc1Π states are,

• Rotational analysis of some of the bands of the orange system of FeO

The orange bands of FeO are excited in a low pressure arc in oxygen and photographed at dispersions of 0·8 and 0·5 Å/mm. respectively. Rotational analysis of five of the bands shows that they involve a1Σ-1Σ transition. The vibrational and rotational constants (in cm.−1) of the upper and lowerΣ states are found to be

In the low-pressure arc it is found that highly excited atomic lines appear very much reduced in intensity in contrast to spectra excited in an arc at atmospheric pressure.

• Infra-red spectral studies of CHF2-CHCl2 and CBrCl2-CBrCl2

The infra-red spectra of two polyhalogenated ethanes, 1, 1-difluoro-2, 2-dichloro ethane and 1, 2-dibromo-1, 1, 2, 2-tetrachloro ethane were obtained in the region of 2·5–38 microns. The spectra of CHF2-CHCl2 were obtained in gas, liquid and solid states and also in solvents of widely varying dielectric constants.

These spectral studies showed that the molecule exists in the form of two rotational isomers. The fundamental modes of the two isomers were identified on the basis of intensity changes from gas to liquid to solid and in solvents of different dielectric constants. The observed infra-red absorption bands have been assigned in terms of the fundamental absorption bands.

Spectra of CBrCl2-CBrCl2 were obtained in the solid and vapour phase and in various solvents. These spectra showed that CBrCl2-CBrCl2 exists only in the trans form. The infra-red spectra, combined with Raman data available from literature was used for complete assignment of the observed absorption bands.

• Rotational analysis of the 0-0 band of the A3 inv-X3 system of ND

The 0-0 band of the A3inv−X3 system of ND was excited in an electrodeless microwave oscillator (2450 Mc./s.) discharge and photographed on a 6·6 meter concave grating spectrograph in the second order at a dispersion of 0·56 A/mm. Twenty-five out of the predicted twenty-seven branches have been identified in the rotational structure of the 0-0 band. From a rotational analysis, the following rotational constants have been determined:

(i)X3state

(ii)A3inv state —

• Isotope shift studies of the ultra-violet and visible bands of P16O and P18O

The spectra of P16O and P18O were excited in sealed discharge tubes containing neon (2–3 mm. pressure), oxygen gas enriched to 65 per cent. of18O and trace amounts of phosphorus vapour and photographed on a 3 m. grating spectrograph at a dispersion of 2·5 Å/mm. Isotope shift studies in theβ-bands confirmed the earlier vibrational scheme of Curryet al. and showed conclusively that the red as well as the violet degraded bands belonged to the sameβ-system. The present studies of isotope shifts also confirmed the vibrational assignments of the extensive ultraviolet bands involving the2Σ−X2Π transition and theγ-bands (A2Σ+−X2Π). In the case of the visible bands, they provided evidence for the first time that the bands at 5585 Å, 5962 Å and 6385 Å belonged to one system and involved 0–0, 0–1 and 0–2 transitions respectively.

• Isotope shift studies of the B3Σ−X3Σ bands of SO

The B3Σ−X3Σ bands of SO were excited in an electrodeless microwave (2450 Mc/s) discharge through trace amounts of sulphur enriched with 37% of34S and oxygen enriched with about 40% of18O. The emission spectra of32S16O,34S16O and32S18O were photographed on a Jarrell-Ash 3·4 m. grating spectrograph at a dispersion of 5 Å/mm. Isotope shift data obtained from the present studies support the revision of the earlier vibrational scheme (Henri and Wolff, 1929; Martin, 1932) by increasingv″-quantum numbering by two units as suggested by Norrish and Oldershaw (1959).

• Rotational analysis of the1Π-X1Σ system of AsN

The1Π-X1Σ bands of AsN were excited by means of radio-frequency discharge through nitrogen and helium and traces of arsenic. The 0-0 band (2784.25 Å) and the 0-1 band (2868.74 Å) were photographed in the third order of a 6.6 meter concave grating spectrograph at a dispersion of 0.38 Å/mm. and analysed for their rotational structure. Perturbations observed in the1Π state were studied in detail.

• Emission spectrum of PrO

The bands of PrO at 8488.95 A and 7986.44 A of system I and at 7662.85 A of system III have been photographed on 6.6 meter concave grating spectrograph at a dispersion of 1.2 A/mm and their rotational structure analysed. They are assigned transitions fromv′ = 0 and 1 levels of A2 Δ5/2 andv′ = 0 level of B2 Δ5/2 to a commonv′’ = 0 level of the ground, X2 Π3/2 state.

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