Photoionization of vapor phase thallium and indium monohalides in the ultraviolet: Absolute cross sections and photofragment spectroscopy by photodetachment of I−

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Abstract
Absolute cross sections for the photoionization of thallium iodide (TlI) and thallium bromide (TlBr) at 193 nm (ℏω=6.4 eV) have been measured to be 2.4×10−17 and 2.2×10−17 cm2, respectively. An upper bound for the ionization cross section of indium monoiodide (InI) at 193 nm was determined to be 7×10−18 cm2. At 248 nm (ℏω=5.0 eV) and 351 nm (ℏω=3.5 eV), the TlI cross section has fallen to 2.6×10−18 and 1.5×10−19 cm2, respectively. The large cross section for TlI at 193 nm arises from photoionization of a bound molecular state. For InI at 6.4 eV and TlI at 5.0 and 3.5 eV, the molecule rapidly dissociates and the smaller cross sections are associated with photoionization of the metal atom. Further experiments combining two excimer lasers with a microwave absorption apparatus were conducted in order to determine the fraction of TlI molecules absorbing a 193 nm photon that produce Tl+–I− ion pairs. By photodetaching electrons from those I− ions remaining after an initial ultraviolet laser pulse, the branching ratio for ion pair production in TlI at 193 nm was measured to be 2%. Approximately 36% of the 193 nm photons absorbed by ground state TlI molecules result in the production of the Tl(7 2S1/2) species and 62% directly produce an excited TlI molecule. The implications of these results for existing atomic photodissociation lasers (Tl: 378 and 535 nm; In: 451 and 410 nm) and column IIIA metal film deposition are discussed.

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