The spectrum of theB²Σ-X²Σ system of the CaF molecule has been photographed in the second order of a 10.6 m concave grating spectrograph with 0.33 Å/mm dispersion. The rotational structure of the (0, 0) and (1, 0) bands has been analysed and the precise molecular constants have been obtained. Using the constants so determined the band origins of a large number of bands with 0 <v′,v″ < 10 have been calculated and used to obtain the accurate vibrational constants forB andX states and these are presented.

Emission spectrum of DyO molecule has been photographed under high resolution in the wavelength region 5000 to 6300 A. The observed bands have been arranged into three different band systems. The rotational structure in the (0, 0) band of system I is partially resolved and analysed. Isotopic shifts have been calculated for various isotopic molecules and compared with observations. Electronic states involved in the transitions have been discussed.

The spectrum of the C²II-X²Σ system of SrF molecule has been investigated under high resolution. The rotational structure in the (0, 0) band has been analysed and the rotational constants for the C²II state have been obtained. The vibrational analysis of this system has been carried out using the band heads from the high resolution spectrogram and also the band origins and the precise vibrational constants have been reported for both the participating states.

The C-X system of diatomic mercury chloride has been re-investigated in emission. The previous vibrational assignments of this system by Horne and others have been confirmed by measurement of the chlorine isotopic shift and improved vibrational constants for the ‘C’ state determined.

The B-A system of CP molecule has been reinvestigated. The rotational structures in the (0, 0) and (1, 1) bands have been photographed in the second order of a 10.6 m grating with 25µ slit width. The molecular constants have been determined using a weighted least squares fit computer program. It is found that the spin-splitting constant in the B-state is negative and not positive as reported by previous workers. An accurate value ofα in the A-state could be determined. The present analysis also suggests that the spin-splitting constant in the ground state of CP should be positive, hence the assignment of theR₁ andR₂ orP₁ andP₂ branches in the B-X system of CP by Barwaldet al should be interchanged.

Laser optogalvanic (LOG) and emission spectra of the N₂ molecule have been recorded at different discharge voltages and gas pressures in the spectral region 5400–6150 Å. It is observed that in the optogalvanic spectrum bands belonging to several systems develop extensively. Under the present discharge conditions bands of the first positive system are predominant. The variation of the signals with pressure and voltage in the two cases is discussed.

Two photon laser optogalvanic spectrum of theD-X system of HgBr molecule has been recorded using Nd-YAG laser pumped dye laser for the first time. A large number of new bands involving higher vibrational levels have been observed. Isotopic heads due to the two bromine isotopes have been observed and used in fixing the vibrational assignment. Vibrational constants for theX andD states of the two isotopic molecules have been determined.

The vibrational overtone spectra of aryl and alkyl C-H stretch vibrations in benzaldehyde have been studied using conventional IR and thermal lensing technique at room temperature. The stretching vibrational frequencyω_e, anharmonicity constantω_ex_e and the dissociation energies of the two C-H bonds have been calculated. The bond length of C-H bond in aryl position has been estimated.

Two photon absorption spectrum ofp-dichlorobenzene has been studied in the spectral region 497–552 nm (one photon wavelength). Bands involving several frequencies of the excited electronic state not detected in the one photon absorption are seen. The observed two photon spectrum indicates that the electronic transition retains, to a large extent, the salient features of the two photon absorption spectrum of benzene and thus confirms chlorine as weak perturber (in the sense of Goodman and Rava [1]).

Fluorescence spectrum of Dy³⁺, Dy³⁺-Ho³⁺, Tb³⁺ and Tb³⁺-Er³⁺ doped in calibo glass have been studied using Ar⁺ and excimer lasers. Non-radiative energy transfer from trivalent dysprosium and terbium (donors) to holmium and erbium (acceptors) respectively has been observed on the basis of decrease in the life time of the levels and reduction in fluorescence intensity of Dy³⁺ and Tb³⁺ on increasing Ho and Er concentrations. The interaction mechanism of donor and acceptor ions is found to be dipole-dipole in both cases. Various parameters such as donor-acceptor distances, non-radiative energy transfer efficiency (η) and energy transfer probability (P_da) have been computed. Stark splitting have also been marked in several intense transition of the two.