Investigation of Vacuum Ultraviolet Photoionization of Methylcyclohexane in Energy Region of 9-15.5 eV

Vacuum ultraviolet(VUV)photoionization and photodissociation of methylcyclohexane have been studied utilizing a reflectron time-of-flight mass spectrometer(RTOF-MS)with synchrotron radiation source.Photoionization efficiency curves(PIEs)of molecule ion C7H14^+ and fragment ions C7H13^+,C6H11^+,C6H10+,C5H10^+,C5H9^+,C4H8^+,C4H7^+,and C3H5^+ were observed.The ionization energy of methylcyclohexane was measured to be(9.80±0.03)eV,and appearance energies of fragment ions were determined from the PIEs.Optimized structures of transitional states,intermediates and product ions were characterized at the B3LYP/6-31G(d)level and the energies were calculated using G3B3 method.Formation channels of dominating fragment ions were proposed.Intramolecular hydrogen migrations and carbon ring-opening were the foremost processes in fragmentation pathways of methylcyclohexane.

A reinvestigation of low molecular weight components in SOA produced by cyclohexene ozonolysis

The ozonolysis of cyclohexene is an important model system for understanding the more complex reaction of O_3 with monoterpenes; however, many previous studies have come to qualitatively different conclusions about the composition of the secondary organic aerosol(SOA)formed in this system. In the present study, the composition of the SOA produced by cyclohexene ozonolysis in the absence of seed aerosols has been investigated online and off-line using synchrotron-based thermal desorption/tunable vacuum ultraviolet photoionization time-of-flight aerosol mass spectrometry(TD-VUV-TOF-PIAMS) in conjunction with a custom-built smog chamber. On the basis of the molecular ions observed by mass spectrometry at 11.5 e V, it was found that dicarboxylic acids, dialdehydes, and cyclic anhydrides are the predominant low molecular weight components in the particle phase. The results also indicated that TD-VUV-TOF-PIAMS coupled with filter sampling is a potentially useful tool for the investigation of SOA composition both in the field and in the laboratory.

Photoionization and Dissociation Study of 2-Methyl-2-propen-1-ol:Experimental and Theoretical Insights

The photoionization and dissociation of 2-methyl-2-propen-1-ol(MPO)have been investigated by using molecular beam experimental apparatus with tunable vacuum ultraviolet synchrotron radiation in the photon energy region of 8.0-15.5 eV.The photoionization efficiency(PIE)curves for molecule ion and fragment ions:C4H8O^+,C4H7O^+,C3H5O^+,C4H7^+,C4H6^+,C4H5^+,C2H4O^+,C2H3O+,C3H6^+,C3H5^+,C3H3^+,CH3O^+,CHO^+have been measured,and the ionization energy(IE)and the appearance energies(AEs)of the fragment ions have been obtained.The stable species and the first order saddle points have been calculated on the CCSD(T)/cc-pvTZ//B3LYP/6-31+G(d,p)level.With combination of theoretical and experimental results,the dissociative photoionization pathways of 2-methyl-2-propen-1-ol are proposed.Hydrogen migrations within the molecule are the dominant processes in most of the fragmentation pathways of MPO.

Experimental and Theoretical Study on Dissociative Photoionization of Cyclopentanone

The dissociative photoionization of cyclopentanone was investigated by means of a reflectron time-of-flight mass spectrometer(RTOF-MS)with tunable vacuum ultraviolet synchrotron radiation in the photon energy range of 9.0~15.5 eV.The photoionization efficiency(PIE)curves for molecular ion and fragment ions were measured.The ionization energy of cyclopentanone was determined to be 9.230.03 eV.Fragment ions from the dissociative photoionization of cyclopentanone were identified as C5H7O+,C4H5O+,C4H8+/C3H4O+,C3H3O+,C4H6+,C2H4O+,C3H6+,C3H5+,C3H4+,C3H3+,C2H5+and C2H4+.With the aid of the ab initio calculations at theωB97X-D/6-31+G(d,p)level of theory,the dissociative mechanisms of C5H8O+are proposed.Ring opening and hydrogen migrations are the predominant processes in most of the fragmentation pathways of cyclopentanone.