Studies of the optical spectra of CaCl and SrF at sub-Doppler resolution

Lines in the (0, 0) bands of the A²Π-X²Σ⁺ and B²Σ⁺-X²Σ⁺ systems of CaCl and the B²Σ⁺-X²Σ⁺ system of SrF have been studied at sub-Doppler resolution by intermodulation spectroscopy. The linewidth was typically 40 MHz (f.w.h.m.). The ¹⁹F hyperfine splitting was resolved in the SrF spectrum and was measured for several rotational lines. The measurements were used in conjunction with the hyperfine parameters for the molecule in the ground state (measured by e.s.r.) to determine the following parameters for the B²Σ⁺ state: b = 12.9 ± 1.6 MHz c = -51 ± 28 MHz. These results suggest that the molecule is ionic, Sr⁺F^-, in the B state. It has not proved possible to resolve ³⁵Cl or ³⁷Cl hyperfine structure in any of the lines studied in either the A-X or the B-X transitions of CaCl. There are pronounced crossover signals in the A-X system which have a negative sign (i.e., opposite to the normal Lamb dip signal). The dependence of these signals on various experimental parameters has been investigated. A density matrix description of the three-level system is presented and solved to 4th order by an iterative method. To this order, the model predicts that the Lamb dip and crossover signals should have the same sign.