Dianxun Wang

A study of HeI photoelectron spectroscopy on the electronic structure of the nitrate free radical NO3

A continuous nitrate free radical (NO3) beam is produced in situ by the pyrolysis of pure gas phase N2O5 at 280 °C (±0.5 °C) in a double-heater inlet system on a double-chamber UPS Machine-II which was built specifically to detect transient species. The HeI photoelectron spectroscopy (PES) of the NO3 radical is recorded for the first time. Five obvious bands emerge on the PE spectrum of the NO3 radical. A very sharp peak with the lowest ionization energy at 12.55±0.01 eV originates from electron ionization of the HOMO for the NO3 radical, corresponding to the NO3+(1A1′)←NO3(2A2′) transition. To assign the bands of the PE spectrum of the NO3 radical, the improved density functional theory (DFT) calculation based on the Amsterdam density functional (ADF) program package has been carried out according to D3h symmetry for the neutral ground state of the NO3 radical and the equilibrium geometries of several ionic states of the cationic species. The ionization energies computed are in reasonable agreement with ...

First Experimental Observation on Different Ionic States of the tert-Butoxy [(CH3)3CO.] Radical

A continuous tert-butoxy (CH3)+CO* radical beam is produced in situ by respective pyrolysis of both (CH3)3CONO at 115(+/-0.5) degrees C and (CH3)3COOC(CH3)3 at 87(+/- 0.5) degrees C. By combining the HeI photoelectron (PE) spectrum with the improved density function theory (DFT) calculations, we have concluded that the (CH3)3CO* radical has C3V symmetry and X2E ground state. The study does not only provide the ionization energies of different ionic states of the (CH3)3CO* radical for the first time, but also the first example in which there have been similar vibrational structures in different ionic states caused by removal of the electron on an orbital. It is also pointed out that (CH3)3CONO is a good source for obtaining the (CH3)3CO* radical beam, and that NO is a stable regent for the active radical. The results will promote the studies in electron spin resonance (ESR) research on the mechanisms of both the initiation of the formation of a new radical and the radical-chain polymerization in which the (CH3)3CO* radical participates.

B3LYP calculations of the potential energy surfaces of the thermal dissociations and the triplet ground state of pyrolysis products XN(x̃3Σ−) for halogen azides XN3 (X: F, Cl, Br, I)

Abstract Mechanisms of XN 3 (X: F, Cl, Br, I) dissociations are proposed based on B3LYP calculated potential energy surfaces. The energy gaps between the ground-state reactants XN 3 ( x 1 A ′ ) and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, XN 3 ( x 1 A ′ )→ XN (a 1 Δ )+ N 2 ( x 1 Σ g + ) . The ISC point, therefore, is considered as a ‘transition state’ of the spin-forbidden reactions, XN 3 ( x 1 A ′ )→ XN ( x 3 Σ − )+ N 2 ( x 1 Σ g + ) . The methods of IRC and topological analysis of electron density are used to predict the thermal dissociation pathway of the reactions studied.

Experimental and theoretical studies on different ionic states of ethylthio CH3CH2S radical

A continuous flowing ethylthio CH3CH2S radical is produced in situ by pyrolysis of CH3CH2SSCH2CH3 at 242(±0.5) °C in a double heater inlet system on a double chamber UPS machine-II which was built specifically to detect transient species. By combining HeI photoelectron spectroscopic (PES) measurement with ab initio GAUSSIAN2 (G2) calculations on different ionic states of the CH3CH2S radical, we have concluded that the CH3CH2S radical has Cs symmetry and the ground state of the CH3CH2S+ cation is the 3A″ state which comes from removal of an electron of the SHOMO 13a′ orbital for the CH3CH2S radical. The PES peak at the lowest ionization energy 9.08 eV with vibrational structure 700±60 cm−1 and corresponding with the G2 computed ionization energy 9.123 eV is designated to the 3A″ ionic state. The removal of an electron of the HOMO 4a″ for the CH3CH2S radical leads to a very sharp peak at 10.31 eV, corresponding to ionization CH3CH2S+ (1A′)←CH3CH2S(X 2A″) and the G2 computed ionization energy 10.322 eV. The...

First experimental observation on different ionic states of the CH3CH2O radical : a HeI photoelectron spectrum of the ethoxy CH3CH2O radical

Abstract A continuous flowing ethoxy CH3CH2O radical beam is produced in situ by pyrolysis of CH3CH2ONO at 223(±0.5)°C. By combining the HeI photoelectron spectrum with the improved density function theory (DFT) calculation, we have concluded that the CH3CH2O radical has Cs symmetry and the ground state of the CH3CH2O+ cation is the 3 A ″ state which comes from removal of an electron of the SHOMO 10a′ orbital for the CH3CH2O radical. Both the photoelectron spectroscopy (PES) experiment and the DFT calculations not only provide another example of exchanging order of the ionic states for the species studied, but also the first example in which there has been almost the same vibrational structure on different ionic states caused by electron ionization on an orbital.

Evidence of the formation and conversion of unstable thionyl isocyanate: Gas-phase spectroscopic studies

Thionyl diisocyanate which is unstable at ambient temperature is generated from a heterogeneous reaction of gaseous thionyl dichloride with silver cyanate and studied for the first time in the gas phase at 298 K. N-isocyanatoformyl sulfinylimide is also observed with photoelectron spectroscopy in the gas phase for the first time. The conversion of thionyl diisocyanate to N-isocyanatoformyl sulfinylimide via 1,3 shift at different temperatures is studied by using photoelectron spectroscopy and mass spectroscopy with the help of theoretical computations. On the basis of combined observations and quantum chemical calculations, possible 1,3-isocyanato shifts and dissociation processes for thionyl isocyanate and its cation have been discussed in detail.

The CH3CH2N: Diradical: Generation Conditions and Determination of its Ionization Energies

We found new pyrolysis conditions for the generation of short-lived radicals. Among these conditions, a molecular sieve is the most important prerequisite, because as a pyrolysis catalyst it effectively reduces the pyrolysis temperature. In the presence of a 20 A molecular sieve and stabilizing NO gas, a CH3CH2N diradical beam with continuous flow has been generated by pyrolysis of CH3CH2N3at 135±0.5 °C. The HeI photoelectron spectrum of the diradical was recorded in situ. The ionization energies determined experimentally and by G2 and DFT calculations correspond to different ionic states of the CH3CH2N+cation. The results indicate that CH3CH2N is a diradical of a 3A″ ground state with Cssymmetry.

Vacuum synthesis and determination of the ionization energies of different molecular orbitals for BrOBr and HOBr

Pure BrOBr and HOBr were synthesized in vacuum by heterogeneous reactions of the dried bromine vapor and Br2/H2O mixture vapors (5:1) with HgO, respectively, and then characterized by He I photoelectron spectroscopy (PES) and augmented by ab initio GAUSSIAN 2 and the outer valence Greens functional calculations. The first PE band at 10.26 eV with vibrational spacing 550±60 cm–1 and the second PE band at 11.23 eV with vibrational spacing 240±60 cm–1 are, respectively, assigned as ionizations of the electrons of the highest occupied molecular orbital (HOMO)(6b1(39)) and the SHOMO(13b2(38)) orbitals of BrOBr. The first PE band at 10.73 eV with vibrational spacing 750±60 cm–1 and the second PE band at 11.56 eV with vibrational spacing 650±60 cm–1 are, respectively, assigned as ionizations of the electrons of the HOMO(6a[double-prime](22)) and the SHOMO(16a[prime](21)) orbitals of HOBr. The study does not only provide vacuum synthesis conditions for preparing pure BrOBr and HOBr, but also provide experimental PES results along with theoretical ionization energies of different molecular orbitals for BrOBr and HOBr.

Experimental and theoretical studies of the electronic structure and the ionization and dissociation processes of trifluoromethyl peroxynitrate

In this work, we present a complete study of the ionization and dissociation processes for trifluoromethyl peroxynitrate (CF3OONO2). CF3OONO2 was generated by UV photolysis of a mixture of (CF3CO)2O, NO2, and O2. The product was detected and characterized by the photoelectron spectroscopy (PES) and photoionization mass spectroscopy (PIMS). The geometric and electronic structures of CF3OONO2 were investigated by the combination of experiments and the density functional and ab initio calculations. It is worthwhile mentioning that drastic changes occur in the geometry of CF3OONO2 after ionization. Due to the removal of one electron from the O-N sigma bond, the COON dihedral angle changes to 180 degrees and as a result, the nonplanar structure becomes planar. And the O-N single bond length increases remarkably, with the positive charge most localized on the NO2 moiety. The experimental first vertical ionization potential is 12.39 eV. Based on the calculated bond dissociation energies, the dissociation pathway was predicted. The calculated results explain the ion intensities observed in the photoionization mass spectrum. The dissociation of O-N single bond is found to be the most favored of the possible dissociation paths for CF3OONO2+.

Molecular and electronic structures of acryloyl isothiocyanate, CH2CHC(O)NCS: a joint experimental and theoretical study

Acryloyl isothiocyanate, CH2CHC(O)NCS, was prepared and studied by IR, Raman, photoelectron spectroscopy (PES), photoionization spectroscopy (PIMS) and theoretical calculations. This molecule was theoretically predicted to prefer the trans-cis (tc) conformation as the most stable conformer, with the CO bond trans to the CC bond and cis to the NCS group. IR and Raman spectra also suggest the presence of the tc conformation only. A theoretical study involving the calculation of the ionization energies using the orbital valence Green’s functional (OVGF/6-311+G(d)) was performed to aid the assignment of the PE spectrum. The first vertical ionization energy of CH2CHC(O)NCS was determined to be 9.89 eV, which is mainly the ionization of the out-of-plane bonding πNCS orbital. Natural population analysis (NPA and NBO) were also performed to investigate the reactivity of CH2CHC(O)NCS.