Strong mutual increase in the efficiency of isotope-selective laser IR dissociation of molecules under nonequilibrium thermodynamic conditions of the compression shock under irradiation in a bimolecular mixture

Abstract

We have revealed a strong (by a factor of 2 to 5) mutual increase in the yield of IR molecular dissociation (by the example of CF2HCl and CF3Br) and a significant (by a factor of 1.5 to 3) lowering of dissociation thresholds in the nonequilibrium thermodynamic conditions of compression shock in the irradiation of the molecules by resonance IR laser radiation in the bimolecular mixture in comparison with their individual irradiation. This opens up the possibility to perform efficient isotope-selective IR dissociation of molecules at lower excitation energy densities (Φ ⩽ 1.5 – 2.0 J cm−2) and thereby to improve the dissociation selectivity. This was demonstrated by the example of chlorine- and bromine-isotope selective dissociation of the specified molecules, which are characterised by quite small (less than 0.25 cm−1) isotope shifts in the IR vibrational absorption spectra excited by laser radiation. The enrichment coefficients K enr(35Cl / 37Cl) = 0.90 ± 0.05 in the residual CF2HCl gas and K enr(79Br / 81Br) in the resultant Br2 product are obtained when the CF2HCl : CF3Br = 1 : 1 molecular mixture and CF3Br molecules, respectively, are irradiated by the 9R(30) CO2 laser line (frequency, 1084.635 cm−1) at an energy density Φ ≈ 1.3 J cm−2.