N.A. Narasimham

Vibrational spectra dihalogenated benzenes. I. In-plane vibrations

Abstract Infrared and Raman spectra of D 4 -ortho, meta and para fluorochloro and fluorobromo benzenes are presented and assignments are given. Some of the bands of H 4 - p -fluorochloro benzene assigned earlier as fundamentals are shown to be due to impurities and alternate assignments are given. The observed frequencies of the H 4 and D 4 molecules are combined in a normal coordinate analysis to obtain a 33-parameter modified valence force field, for the in-plane vibrations, with an average difference of ±0.8% between observed and calculated frequencies. The normal coordinate analysis shows that many of the previous assignments of the ring modes ν 1 , ν 6 , and ν 12 for disubstituted benzenes are not very reliablie. Revised assignments with good correlation with the corresponding benzene modes are given.

Isotope shift studies in the spectra of NS and PS

Abstract The emission spectra of NS and PS have been excited in a microwave (2450 Mcps) discharge using enriched 34 S. Isotope shifts observed for the β-, γ- and the two new band systems involving 2 Π- X 2 Π (2650–2880 A) and 2 Σ- X 2 Π (2320–2400 A) transitions of NS, have been found to confirm the earlier vibrational assignments. In the band systems of PS, several new bands have been found which form an extension of the ultraviolet system while, in the case of the visible bands, the earlier assignment of v″ -values has to be increased by one unit.

Vibrational spectra and normal coordinate analysis of dihalogenated benzenes. II. Out-of-plane vibrations

Abstract Assignments of the out-of-plane fundamental modes for D 4 -ortho, meta and para fluorochloro and fluorobromo benzenes are given. A normal coordinate analysis, employing the 94 observed frequencies of the H 4 and D 4 molecules is carried out to obtain a 16-parameter Valence Force Feld, with an average difference of ±1.2% between observed and calculated frequencies. Unique assignments are obtained in the spectra of D 4 -compounds for several of the weak or overlapping bands assigned as fundamentals in the H 4 -compounds.

Intensity measurement of laser-excited fluorescence in the B3Πu(0+)-X1Σg+ system of diatomic lodine

Abstract Fluorescence was excited in the B3Πu(0+)-X1Σg+ system of diatomic iodine by means of the 5145-A line of an Ar+ laser and the 6328-A line of a HeNe laser. The resulting spectrum was recorded on a SPEX double monochromator and a quantitative measurement of the intensities was carried out. The variation of the electronic transition moment M( R ) with R centroid observed by us shows a behavior similar to what has been reported earlier.

Predissociations in the d1Σ+-c1Π bands of NH

Abstract During the course of the rotational analysis of the bands of the d 1 Σ + - c 1 Π system of NH, a sudden breaking-off of rotational structure was observed in the 0-0 band (2557 A) at J ″ ≥ 24 and in the 1-1 band (2516 A) at J ′ ≥ 16. These are attributed to (i) a predissociation of the initial d 1 Σ + due to an interaction of a repulsive 1 Π state, and (ii) “dissociation by rotation” of the c 1 Π state. From the energy of dissociation of the c 1 Π state, the dissociation energies of other known singlet states of NH are determined.

Normal coordinate analysis of the out-of-plane vibrations of o, m, p- fluorochloro and fluorobromo benzenes

A normal coordinate analysis of the out-of-plane vibrations of o, m, p- fluorochloro and fluorobromo benzenes was made dividing the six molecules into two sets. The frequencies of the assigned fundamentals were fitted to least-squares by a 12 parameter valence force field. Several of the assignments made for these molecules by earlier workers were revised.

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.