The effect of dielectronic recombination as an excitation process in the intensity of solar x-ray lines of calcium ions is investigated. It is found that x-ray line intensities are enhanced by 15% to 88% with the inclusion of dielectronic recombination as an excitation mechanism.

Einstein A-coefficients for the electric-dipole transitions between the rotational levels up to 785 cm⁻¹ in the ground vibrational state of D₂O are calculated. The A-values are used to compute the mean-radiative life-times of the levels.

We present a new method for the evaluation of the RKR potential-integrals for diatomic molecules. This method is straightforward and fast, and the calculations can be performed to an accuracy better than any other method.

When observed spectrum of a diatomic molecule is expressed in terms of the Dunham coefficients $Y_{00}$, $Y_{10}$, $Y_{20}$, $Y_{01}$, and $Y_{11}$ only, dissociation energy of the molecule is given by $Y_{00} + Y^{2}_{10}/(-4Y_{20})$. Kaur and Mahajan [1] have used the Dunham coefficients $Y_{10}$, $Y_{20}$, $Y_{01}$, and $Y_{11}$, for 15 vibrational states of 12 diatomic molecules ($Y_{00}$ is zero for the cases accounted for), but their dissociation energy cannot be reproduced by the expression $Y^{2}_{10}/(-4Y_{20})$. Probable reason for the discrepancy has been discussed.

Laboratory formation of four isomers of C⁵H² molecule is reported and detection of the ring-chain isomer (isomer 1) of C₅H₂ in cosmic objects has been suggested. For identification of a molecule in cosmic objects, one of the required input data is EinsteinA-coefficients (radiative transition probabilities) for the molecule. Here, we report EinsteinA-coefficients for electric dipole transitions in the ring-chain isomer of C₅H₂ among the rotational levels of the ground electronic and ground vibrational states up to 21 cm⁻¹.

We suggest that Si₂C molecule may be identified in astronomical objects through its transitions 4₁₄ → 5₀₅, 5₁₅ → 6₀₆, 2₁₂ → 3₀₃, 3₁₃ → 4₀₄, and 1₁₁ → 2₀₂ at 15.9, 5.1, 33.6, 24.9, and 42.3 GHz in absorption even against the cosmic 2.7 K background, in a region having low temperature. The absorption phenomenon is found rather large in the first two transitions. Dependence of results on the set of molecular parameters is discussed.

Statement of Kaur and Mahajan [1] about the definition of Δ used by Chandra [2] is not correct. Even if we take Δ = μω_e²r_e²/2D_e, the relation between Δ and G(=8ω_ex_e/B_e) is obtained as Δ = 4.21452856G, provided the vibrational energy of a diatomic molecule is expressed in terms of limited Dunham coefficients, Y₁₀, Y₂₀, Y₀₁ and Y₁₁. This relation is still different from that of Kaur and Mahajan [3]

Wiesenfeld and Faure investigated rotational quenching of H$_2$CO by molecular hydrogen where they considered 40 rotational levels of $o$-H$_2$CO and 41 rotational levels of $p$-H$_2$CO. Data on energies of rotationallevels of the molecule are fundamental in the investigation. We have found that the sequence of levels reported by Wiesenfeld and Faure is not as per convention of molecular physics. Their results are also available on the website: http://home.strw.leidenuniv.nl/∼moldata/datafiles/ph2co-h2.dat, where the collisional transitions are shown even between the levels having equal energies. Data for such transitions should not be there.