Isotope effects in the quenching of electronically excited atoms. Quenching of I(52P½) by methane and deuteromethanes studied by time-resolved resonance fluorescence

Abstract

The quenching of electronically excited iodine atoms, I(5²P_½), by CH₄, CD₃H and CD₄ has been studied using time-resolved resonance fluorescence: k(CH₄)=(9.4 ± 0.4)× 10^–14 cm³ molecule^–1 s^–1k(CD₃H)=(5.4 ± 0.4)× 10^–14 cm³ molecule^–1 s^–1k(CD₄)=(2.2 ± 0.4)× 10^–15 cm³ molecule^–1 s^–1 These isotope effects are shown to be consistent with a mechanism involving resonant electronic to vibrational + rotational (E–VR) energy transfer. A calculation, based on long-range coupling between transition multipole moments, is presented for the quenching of I(5²P_½) by CH₄ and is in good agreement with the experimental result, supporting this mechanism for resonant E–VR transfer.