Double resonance spectroscopy of the $B^{″}\overline{B}$ ${}^1\Sigma _u^{+}$ state of ${\mathrm{H}}_2$

Double resonance spectroscopy via the $EF{}^1\Sigma _g^{+},{\nu }_{EF}^{\prime }=6,J^{\prime }$ state has been used to probe the rovibrational structure of the ungerade double-well $B^{″}\overline{B}$ ${}^1\Sigma _u^{+}$ state of ${\mathrm{H}}_2$. Transitions to the $B^{″}\overline{B}{}^1\Sigma _u^{+},{\nu }_{\overline{B}}=17-35,J=0-4$ levels of the outer-well and to the ${\nu }_{B^{″}\overline{B}}=46-50,J=0-4$ levels of the combined inner and outer wells above the barrier have been recorded by detecting both molecular and atomic ion production as a function of energy by using a time of flight mass spectrometer. Theoretical energy calculations incorporating the most recent potential curves have been used to aid in the assignment of observed transitions. Over 70 new rovibrational term energies are reported. Where comparisons are possible, good agreement is observed between the experimental measurements reported here and those of previous measurements. While significant perturbations are observed in the energy region above the double-well barrier, assignments to states with dominant inner and outer-well characteristics can still be made. Distinct dynamical behaviors of the levels below, at, and above the barrier have also been observed.

Figure 1

Excitation scheme and adiabatic potential energy curves of the relevant states of ${\mathrm{H}}_2$ and ${{\mathrm{H}}_2}^{+}$.

Figure 2

Schematic of the experimental arrangement.

Figure 3

${\mathrm{H}}^{+}$ and ${\mathrm{H}}_2^{+}$ probe spectra in the energy region of the $P\left(2\right)$ and $R\left(2\right)$ branches of the $B^{″}\overline{B}{}^1\Sigma _u^{+}$, ${\nu }_{\overline{B}}=18,J\leftarrow EF{}^1\Sigma _g^{+},{\nu }_{EF}^{\prime }=6,J^{\prime }=2$ transition.

Figure 4

${\mathrm{H}}^{+}$ probe spectra showing transitions to several levels of the $B^{″}\overline{B}{}^1\Sigma _u^{+}$ state in an energy region above the double-well barrier of the $B^{″}\overline{B}{}^1\Sigma _u^{+}$ state. The (a)–(d) labels indicate signals obtained via excitation of the $Q\left(0\right)$, $Q\left(1\right)$, $Q\left(2\right)$, and $Q\left(3\right)$ $EF{}^1\Sigma _g^{+},{\nu }_{EF}^{\prime }=6\leftarrow X{}^1\Sigma _g^{+},{\nu }^{″}=0$ pump transitions, respectively.

Figure 5

Experimental term energies as a function of $J(J+1)$ using the proposed assignments given in Table .