Knowledge Bank

Our recent measurement of the infrared spectrum of CH$\mathrm{5+}$ in the C-H stretching region (2825-3100 \wn) has provided new insight into the behavior of this highly fluxional molecule. Examining four-line combination differences matched to 40 MHz, we have tentatively assigned two vibrational band origins near 2950 and 3025 \wn. Using the most complete ab initio calculations to date, these features can be assigned to symmetric and asymmetric stretches of the hydrogen-like CH$2$ component of CH$\mathrm{5+}$. Furthermore, we have assigned several ro-vibrational progressions within these bands. Fits of these lines to a simple spherical-top Hamiltonian yield a ground-state rotational constant of approximately 3.92 \wn, in agreement with theoretical predictions. With these initial results, the mystery of CH$\mathrm{5+}$ is beginning to be unraveled.