Mixed quantum-classical approach to the calculation and assignment of the time- resolved photoelectron spectra

Abstract

Vremenski razlučena fotoelektronska spektroskopija (TRPES) jedna je od najprikladnijih pobudno-testnih tehnika za praćenje spregnute nuklearne i elektronske dinamike. Med̄utim, kako bi se molekulska dinamika mogla "vidjeti" u spektru, potrebne su teorijske simulacije i asignacije spektara. U ovom je radu klasični formalizam ulazno-izlaznog probira primjenjen na TRPES tehinku. Osmišljena je i implementirana pragmatična metodologija izvrednjavanja izraza, koja se temelji na multireferentnom opisu vezanih elektronskih stanja, miješanoj kvantno-klasičnoj simulaciji neadijabatske dinamike te opisu fotoionizacijskog kontinuuma unutar teorije funkcionala gustoće sa statičkom izmjenom. Uz to, osmišljen je i implementiran jednostavan algoritam za asignaciju TRPES spektra u terminima elektronskih karaktera, temeljen na dijabatizaciji vezanih elektronskih stanja. Ukupna metodologija je primjenjena na dva prototipna fotoinducirana procesa, internu konverziju u pirazinu te otvaranje prstena u cikloheksa-1,3-dienu. Nova saznanja o mehanizmima proučavanih procesa su prezentirana i raspravljena. Dodatno, simulacijama neadijabatske dinamike proučeni su i mehanizmi eliminacije dušika iz diazometana prilikom pobude u prvo i drugo pobud̄eno stanje.Time-resolved photoelectron spectroscopy (TRPES) has proven to be one of the most convenient pump-probe techniques for monitoring the coupled nuclear and electronic dynamics. However, in order to "see" the molecular dynamics in the spectrum, the theoretical simulations and assignment of the spectra are needed. In this work, the classical doorway-window formalism has been applied to the TRPES technique. A pragmatic methodology of evaluation of the expression has been designed and implemented. It consists of multireference treatment of bound electronic states, a mixed quantum-classical simulation of nonadiabatic dynamics and static-exchange DFT treatment of the photoionization continuum. Also, a simple procedure of TRPES assignment in the terms of electronic characters, based on the diabatization of the bound electronic states, has been designed and implemented. The methodology as a whole has been applied on two prototype photoinduced processes: internal conversion in pyrazine and the ring-opening reaction in cyclohexa-1,3-diene. New insights in the mechanisms of the studied processes are presented and discussed. In addition, the mechanisms of nitrogen elimination from diazomethane during excitation to the first and second excited state were studied by simulations of nonadiabatic dynamics