Knowledge Bank

Using a Ti-sapphire laser and a radiofrequency wave guide in combination with a fast, mass-selected beam of $He2$ in the meta-stable a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ state, we have measured the fine structure splittings in the a $(\nu =0,N=25,27,29$ and $\nu =2,N=7,9,11)$ levels to a precision better than 15 kHz. The experimental spin-spin and spin-rotation coupling parameters $\lambda$ and $\gamma$ (in MHz) are well represented as second order polynomial in the internuclear separation, R (in atomic units): [ \lambda(R)=-1101.221+1349.2241(R-2)-427.22254(R-2)^{2} ] and [ \gamma(R)=-2.39823+4.70583(R-2)-3.27895(r-2)^{2} ] Using these polynomial and the nuclear wavefunctions calculated from the a-state potential of Yarkony [1], we can reproduce the experimental values of $\lambda$ and $\gamma$ within 0.01 MHz. The laser excites molecules from the a-state to quasibound levels in the $c\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$ state, which decay by tunneling through the potential barrier of the c-state. The experimental linewidths agree well with those calculated using the empirical c-state potential of Lorents et al. [2]