Molecular hydrogen is the dominant molecular species present in the interstellar medium and has an important role in the cooling of shocks that are associated with star formation. The two mechanisms of cooling are collisional excitation followed by quadrupole emission and collisional dissociation. Modelling the role of dissociation in this cooling needs detailed information on the state specific dissociation rate coefficients. The initial goal of this research was to compare the trajectory outcomes on the Hinde potential energy surface (PES) with those on the BMKP2 PES to assess whether it is required to do extensive and more expensive calculations to determine state specific rate coefficients for dissociation of H2 + H2 to supersede those previously determined with the BMKP2 surface. A phenomenon of double dissociation was unexpectedly identified within the Hinde PES, despite the absence of sufficient energy for such an occurrence. These results prompted a comprehensive analysis of the Hinde PES, which in turn involved an exploration of the regions that exhibit unphysical behavior. This detailed examination unveiled problematic aspects of the potential energy surface. As a result of this, it has been determined that the Hinde PES is unsuitable for calculating dissociation rate coefficients for H2 + H2.
We examine the relationship between stock returns and components of idiosyncratic volatility—two volatility and two covariance terms— derived from the decomposition of stock returns variance. The portfolio analysis result shows that volatility terms are negatively related to expected stock returns. On the contrary, covariance terms have positive relationships with expected stock returns at the portfolio level. These relationships are robust to controlling for risk factors such as size, book-to-market ratio, momentum, volume, and turnover. Furthermore, the results of Fama-MacBeth cross-sectional regression show that only alpha risk can explain variations in stock returns at the firm level. Another finding is that when volatility and covariance terms are excluded from idiosyncratic volatility, the relation between idiosyncratic volatility and stock returns becomes weak at the portfolio level and disappears at the firm level.
