THE ABSORPTION SPECTRUM AlCl BETWEEN $1300 AND 2500 \AA$

Abstract

Observations of the absorption spectrum of AlCl has led to the identification of five new electronic systems in the region between $1500 and 1900 \AA$. The strength of the transitions from the ground state, $known^{1}$ to be $X ^{1}\Sigma^{+}$, suggests strongly that each of the newly observed states is a singlet state. Vibrational assignments were based on band head measurements of the $Al^{35} Cl/Al^{37}Cl$ isotopes and/or correlation with the known ground state vibrational frequencies. We have designated the first new system, near $1839 \AA$, as the B - X system since no new bands were observed in absorption between this system and the $A ^{1} \Pi = X ^{1}\Sigma^{+}$ system at $2600 \AA$, The B - X and B - X system display extensive rotational structure, but the C - X, D - X, and F - X systems were not sufficiently resolved to permit rotational analyses. Rotational analyses of the 1-0, 0-0, and 0-1 bands of the B - X system establish that the upper state is a $^{1}\Sigma^{+}$ state with the following constants $(in cm^{-1}): \nu_{00} = 54 385.1, \Delta G_{1} = 583.0. B_{0} = 0.2641, B_{1} = 0.2627$, and $D_{0} D_{1} = 2.1 \times 10^{-7}$. The apparance of Q heads in the E - X system requires that the upper state be $^{1}\pi$, and the separation between Q and P heads permits an estimate of the upper state B values for $\nu^{1} = 0 = 5$. Efforts are continuing for a full rotational analysis of these bands. Work is also underway on the remaining band systems which have extensive but overlapping structures.