Access Type

Open Access Dissertation

Date of Award


Degree Type


Degree Name




First Advisor

Wen Li

Second Advisor

Arthur G. Suits


This dissertation focuses on unimolecular dissociations of molecules under colissionless conditions with IRMPD. IRMPD was used as the dissociation technique in these studies since roaming type dissociations predominates from the ground electronic state. DC slice imaging was used with REMPI as the detection technique to study the products in a state selective manner to understand the nano scale dynamics of unimolecular dissociations. In the investigation of photodissociation dynamics of nitromethane and methyl nitrite with IRMPD, nitromethane show very low translational energy release of the photofragments and resemble the “roaming” pathway in the dissociation of nitromethane. The difference in the intensities of the averaged images show the presence of the lambda doublet propensity during the dissociation of nitromethane. In contrast, methyl nitrite does not show lambda doublet propensity while giving extra few kcal/mol during the dissociation into products relative to nitroethane supporting the conclusion of roaming mediated isomerization of nitromethane into methyl nitrite prior to dissociation. The studies were extended for the C-2, C-3, and C-4 systems to generalize the idea of isomerization of nitro compound to nitrite prior to dissociation. The studies suggested that the C-2 and the C-3 system predominates via the isomerization channel to give NO as a product despite the fact that the CME channel threshold is lower. Nitrobutane, however, show some distinct behavior than the C-2 and C-3 systems. The reason may be the presence of a 6-membered transition state or another pathway for the C-4 system which is not available for the C-2 and C-3 systems. Even though roaming reactions are more popular from the ground electronic state dissociations, NO3 molecule was reported roaming dissociations on an excited electronic. The two experimental sets carried out to understand the photodissociation of NO3 shows the roaming type dissociation of both D0 and D1 surfaces while suggesting a possible different dissociation pathway for the excited NO3. In the study of IRMPD of vinyl chloride, translational energy distributions suggest that vinyl chloride dissociate via the 3-C transition state while giving vibrationally and rotationally cold vinylidene as a product.