Selectivity decline at high pulse repetition rates in laser isotope separation of carbon-13 due to energy accumulation

Abstract

Laser isotope separation has emerged as a promising technique for the selective separation of ¹³C isotope, offering a simple setup, high selectivity, and low energy consumption. Contrary to a previous study, we found that increasing the pulse repetition rate to enhance production rate actually leads to a decrease in ¹³C selectivity. This decline is attributed to energy accumulation within the irradiated region, inducing thermal excitation, increased molecular collision frequency and non-selective dissociation related to V-V, V-R and V-T energy transfers. To eliminate these negative effects, we recommend using an absorption cell with a gas exchange system to guarantee that each laser pulse interacts with fresh gas molecules. The selectivity decline can also be mitigated by using a vibrational relaxer, such as argon. Another alternative to maintain selectivity is increasing the wavelength. The underlying mechanisms are further elaborated through a perspective of molecular dynamics.