3 Einstein A-coefficients

In a representation in which the axis of quantization is along a-axis of inertia, the expression for the line strength for a-type molecule is given by

$$S(J^\prime_{\tau^\prime} \rightarrow J_\tau) = \mu^2 (2J + 1... ... K}g^{J^\prime}_{\tau^\prime K} C^{J^\prime K}_{JK10} \Big]^2$$ (2)

where the C's are Clebsch-Gordan coefficients. The transition probabilities follow directly from the line strength (Chandra & Sahu 1993)

$$A(J^\prime_{\tau^\prime} \rightarrow J_\tau) = \frac{64 \pi^... ...3(2J^\prime + 1)} S(J^\prime_{\tau^\prime}\rightarrow J_{\tau})$$ (3)

where $\nu$ corresponds to the energy difference of the two levels. The rotational constants and quartic and sextic centrifugal distortion coefficients taken for Silicon Dicarbide from Bogey et al. (1984) are presented in Table 1. Table 1 carries also the constants for ²⁹SiC₂ and ³⁰SiC₂ isotopomers. The distortional constants for ²⁹SiC₂ and ³⁰SiC₂ are the same as for ²⁸SiC₂ (Cernicharo et al. 1986). The computed value of Einstein A-coefficients between the levels up to 51 cm^-1 are given in Tables 2, 3 and 4 for ²⁸SiC₂ (Silicon Dicarbide), ²⁹SiC₂ and ³⁰SiC₂, respectively for ortho-rotational transitions in the ground vibrational state. Here, the primed parameters correspond to the upper level of the transition whereas the unprimed correspond to the lower level of transition. Table 5 shows the radiative life times of the levels which are calculated by using Einstein A-coefficients.