Relaxation and spectroscopy of CaCl in seeded supersonic beams

The rotational and vibrational relaxation of a calcium-monochloride beam, seeded in He, Ar and Kr has been investigated by laser-induced fluorescence. The rotational distributions cannot be described by a single temperature. A two-parameter formula is given which represents the measured distributions and which is characterized by local temperatures from 30 to 200 K depending on the rotational states and the expansion conditions with source temperatures of T₀ = 1320 K and T₀ = 1520 K. The effective cooling increases from He to Ar as carrier gases. In contrast, the vibrational distributions could be represented by Boltzmann distributions with temperatures of 1400 to 589 K. The order of vibrational cooling goes from Ar < He < Kr. Parts of the CaCl X-B spectrum have been recorded with high resolution. The attempt to identify the measured lines reveals that the best molecular constants for this system do not reproduce all lines of Ca³⁵Cl and especially not those of Ca³⁷Cl within the needed accuracy. The spin-rotational constant of the B²Σ state is determined to γ₀₀ = ?0.06513 (9) with a 2σ uncertainty.