Nanosecond Laser Induced Transient Absorption Flash Photolysis Experiment for Undergraduate Physical Chemistry

Research laboratories commonly perform studies of fast chemical reactions with lasers using fast and ultrafast spectroscopy. However, students at the level of undergraduate physical chemistry laboratory course rarely experience with fast spectroscopy techniques. Therefore, the objective of this laboratory experience is to introduce this student population to fast spectroscopy techniques by using a modular nanosecond laser induced transient absorption spectro-kinetic photometer (NLTRAS) in a Physical Chemistry laboratory course. The experimental setup proposed illustrates fundamental principles and instrumentation of fast spectroscopy and transient intermediates characterization, transient kinetics, and electronic spectroscopy appropriate for undergraduate physical chemistry level. The advantage of using the NLTRAS to generate the transient absorption spectra to study the kinetics of reactive intermediates is demonstrated by the laser induced triplet-triplet transient absorption spectrum measurements of thioxanthone in acetonitrile and of thiomethylpromazine in water. These molecules are chosen because they have a high intersystem crossing quantum yield (ΦT>0.6) necessary for an adequate signal to noise ratio. In addition, alternative experiments with various learning objectives are recommended. Fundamental knowledge on spectroscopic techniques like NLRTAS will be an asset to those students pursing graduate studies and also for those that decide a career in industry.