I am studying the chemical reaction of radicals by computational chemistry software. I just want to know what is the rules for multiplicity. I have two radicals for which, the ground state of one is a doublet and the other is a triplet. A chemical reaction between them is possible or not, if a chemical reaction is possible then in what multiplicity the reaction will proceed. what multiplicity should I use in my input file?
With respect to the question "if a chemical reaction is possible or not", here is some background material on oxygen species.
In particular, Singlet oxygen apparently reacts with oxygen (also referred to as dioxygen) creating a very strong (but transient) oxidizing atomic oxygen.
Examples of possible reactions of interest, including atomic oxygen, can be found, per Equations (1) to (5), from a work discussing graphene patterning here: http://olab.physics.sjtu.edu.cn/papers/2017/29.Huan%20Yue_PCCP_2017.pdf , where apparently, O(3P) is created from severe collision quenching of O(1D) atom with air or oxygen and acts as the major oxidant in the work by Huan Yue and colleagues ‘Exploring the working mechanism of graphene patterning by magnetic-assisted UV ozonation’.
Note, O(3P) is also known as highly reactive ground-state 3P oxygen and a form of atomic oxygen.
Also be mindful, in the real world if any water vapor is present, Singlet oxygen reacts with H2O forming H2O2, where O(1D) has a half-life of around 45 minutes.