Energy levels, radiative rates and electron impact excitation rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV

Abstract: We report calculations of energy levels, radiative rates and electron impact excitation cross sections and rates for transitions in He-like Ga XXX, Ge XXXI, As XXXII, Se XXXIII and Br XXXIV. The {\sc grasp} (general-purpose relativistic atomic structure package) is adopted for calculating energy levels and radiative rates. For determining the collision strengths, and subsequently the excitation rates, the Dirac Atomic R-matrix Code ({\sc darc}) is used. Oscillator strengths, radiative rates and line strengths are reported for all E1, E2, M1 and M2 transitions among the lowest 49 levels of each ion. Additionally, theoretical lifetimes are provided for all 49 levels of the above five ions. Collision strengths are averaged over a Maxwellian velocity distribution and the effective collision strengths obtained listed over a wide temperature range up to 10$^{8}$ K. Comparisons are made with similar data obtained using the Flexible Atomic Code ({\sc fac}) to highlight the importance of resonances, included in calculations with {\sc darc}, in the determination of effective collision strengths. Discrepancies between the collision strengths from {\sc darc} and {\sc fac}, particularly for some forbidden transitions, are also discussed. Finally, discrepancies between the present results for effective collision strengths with the {\sc darc} code and earlier semi-relativistic $R$-matrix data are noted over a wide range of electron temperatures for many transitions in all ions.