4 Conclusion
In this work, we presented SAC-CI/Monopole Approximation calculations of the
photoionization spectra of four energetic molecules having at least one NO 2
group. For one of them, nitromethane, the results are new.
Nitromethane has two almost degenerate conformers. The convoluted spectra of
the two conformers showed very good agreement with the measured spectrum. The
1st I.P. also agreed very well with the experiment, but the character of the state was
not the result of ionizing the electron from the HOMO as would be expected from
Koopmans’ theorem. For other nitromethane I.P.’s, there is good agreement but
also some discrepancy with experimental values.
For the four energetic molecules, we discussed the common features of the
computed photoionization spectra. For the nitramide, N,N-dimethylnitramine and
nitromethane molecules, the agreement with the experimental spectra is very good.
Concerning the I.P’s values of these three molecules, in general the agreement is
very good with measured I.P’s, especially with the 1st I.P., although there some
discrepancies for the higher I.P’s of nitromethane. The comparison of our I.P’s
values and character of the ionized states shows important differences when compared with the corresponding properties according to the Koopmans’ theorem.
Moreover, even for the 1st I.P., the inclusion of correlation via the SAC-CI wave
function can lead to a different character of this state compared with the single
HOMO ionization according to Koopmans’.
To sum up, we have shown that the SAC-CI wave function combined with the
Monopole Approximation can provide assignments, I.P.’s and spectral information
in good agreement with experimental data. Furthermore, we could highlight is this
work that the indiscriminate use of the Koopmans’ both to interpret and obtain I.P’s
values can lead to severe misinterpretations.
Acknowledgments We thank Faperj, CNPq and Capes, Brazilian Agencies, for support of this
work.
References
1. Ali AN, Son SF, Asay BW, Sander RK (2005) Importance of the gas phase role to the
prediction of energetic material behavior: an experimental study. J Appl Phys 97:7
2. Anders G, Borges I (2011) Topological analysis of the molecular charge density and impact
sensitivy models of energetic molecules. J Phys Chem A 115:9055–9068
3. Attina M, Cacace F, Ciliberto E, Depetris G, Grandinetti F, Pepi F et al (1993) Gas-phase ion
chemistry of nitramide—a mass-spectrometric and ab-initio study of H2N-NO2 and the
H2N-NO2radical+, [H2N-NO2]H+, and [HN-NO2]- ions. J Am Chem Soc 115:12398–12404
4. Bernstein ER (2005) Role of excited electronic states in the decomposition of energetic
materials. In: Shaw RW, Brill TB, Thompson DL (eds) Overviews of recent research on
energetic materials, vol 16. World Scientific, Singapore, p 161
156
I. Borges Jr. and E. Uhl
In this work, we presented SAC-CI/Monopole Approximation calculations of the
photoionization spectra of four energetic molecules having at least one NO 2
group. For one of them, nitromethane, the results are new.
Nitromethane has two almost degenerate conformers. The convoluted spectra of
the two conformers showed very good agreement with the measured spectrum. The
1st I.P. also agreed very well with the experiment, but the character of the state was
not the result of ionizing the electron from the HOMO as would be expected from
Koopmans’ theorem. For other nitromethane I.P.’s, there is good agreement but
also some discrepancy with experimental values.
For the four energetic molecules, we discussed the common features of the
computed photoionization spectra. For the nitramide, N,N-dimethylnitramine and
nitromethane molecules, the agreement with the experimental spectra is very good.
Concerning the I.P’s values of these three molecules, in general the agreement is
very good with measured I.P’s, especially with the 1st I.P., although there some
discrepancies for the higher I.P’s of nitromethane. The comparison of our I.P’s
values and character of the ionized states shows important differences when compared with the corresponding properties according to the Koopmans’ theorem.
Moreover, even for the 1st I.P., the inclusion of correlation via the SAC-CI wave
function can lead to a different character of this state compared with the single
HOMO ionization according to Koopmans’.
To sum up, we have shown that the SAC-CI wave function combined with the
Monopole Approximation can provide assignments, I.P.’s and spectral information
in good agreement with experimental data. Furthermore, we could highlight is this
work that the indiscriminate use of the Koopmans’ both to interpret and obtain I.P’s
values can lead to severe misinterpretations.
Acknowledgments We thank Faperj, CNPq and Capes, Brazilian Agencies, for support of this
work.
References
1. Ali AN, Son SF, Asay BW, Sander RK (2005) Importance of the gas phase role to the
prediction of energetic material behavior: an experimental study. J Appl Phys 97:7
2. Anders G, Borges I (2011) Topological analysis of the molecular charge density and impact
sensitivy models of energetic molecules. J Phys Chem A 115:9055–9068
3. Attina M, Cacace F, Ciliberto E, Depetris G, Grandinetti F, Pepi F et al (1993) Gas-phase ion
chemistry of nitramide—a mass-spectrometric and ab-initio study of H2N-NO2 and the
H2N-NO2radical+, [H2N-NO2]H+, and [HN-NO2]- ions. J Am Chem Soc 115:12398–12404
4. Bernstein ER (2005) Role of excited electronic states in the decomposition of energetic
materials. In: Shaw RW, Brill TB, Thompson DL (eds) Overviews of recent research on
energetic materials, vol 16. World Scientific, Singapore, p 161
156
I. Borges Jr. and E. Uhl