Photofragmentation of Tetranitromethane: Spin ... - ACS Publications

Jun 16, 2017 - Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States. ‡. Department of Coatings and Pol...
3 downloads 0 Views 731KB Size
Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Letter

Photofragmentation of Tetranitromethane: Spin-Unrestricted Time-Dependent Excited-State Molecular Dynamics Yulun Han, Bakhtiyor Rasulev, and Dmitri S. Kilin J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.7b01330 • Publication Date (Web): 16 Jun 2017 Downloaded from http://pubs.acs.org on June 17, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

The Journal of Physical Chemistry Letters is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

1

Photofragmentation of Tetranitromethane: Spin-Unrestricted Time-Dependent Excited-

2

State Molecular Dynamics

3

Yulun Han,†,‡ Bakhtiyor Rasulev,∥ and Dmitri S. Kilin*,†,‡

4



5

∥Department

6

58102, United States

7



8

United States

Department of Chemistry, University of South Dakota, Vermillion, South Dakota 57069, United States of Coatings and Polymeric Materials, North Dakota State University, Fargo, North Dakota

Department of Chemistry and Biochemistry, North Dakota State University, Fargo, North Dakota 58108,

9 10

Abstract:

11

In this study, the photofragmentation dynamics of tetranitromethane (TNM) is explored by a spin-

12

unrestricted time-dependent excited-state molecular dynamics (u-TDESMD) algorithm based on Rabi

13

oscillations and principles similar to trajectory surface hopping, with a mid-intensity field approximation.

14

The leading order process is represented by the molecule undergoing cyclic excitations and de-excitations.

15

During excitation cycles, the nuclear kinetic energy is accumulated to overcome the dissociation barriers

16

in the reactant and a sequence of intermediates. The dissociation pathway includes the ejection of a NO2

17

group followed by the formation of NO and CO. The simulated mass spectra at the ab initio level, based

18

on the bond length in possible fragments, are extracted from simulation trajectories. The recently

19

developed methodology has the potential to model and monitor photoreactions with open-shell

20

intermediates and radicals.

21

1 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

22

Tetranitromethane (TNM), designated as C(NO2)4, is an oxygen-rich methane derivative.

23

The oxygen weight per unit volume of TNM is nearly the same as that of liquid oxygen itself.1

24

TNM is a volatile liquid at ambient conditions with a 399 K normal boiling point and a 287 K

25

melting point.1-2 The structure of TNM consists of four equivalent nitro groups around the

26

tetrahedral carbon center.2-3 One nitro group of TNM shows great mobility in chemical

27

reactions.2,

28

propellant.1,

29

with hydrocarbons.4 A plant working upon the manufacture of TNM on an industrial scale was

30

destroyed by an explosion in 1953.1 There have been many experimental investigations on the

31

pyrolysis and photolysis of TNM.3, 8-10 In addition, extensive simulations have been carried out

32

to study the thermal or photochemical decomposition of the simplest nitroalkane e.g.

33

nitromethane (NM).11-16 For instance, Fileti et al. reported the detonation kinetics and explosion

34

reaction of NM computed by reactive force field (ReaxFF) molecular dynamics (MD)

35

simulations.11 However, to our knowledge, theoretical studies addressing the photodissociation

36

of TNM due to photoinduced electronic transitions are limited.

4

TNM has a wide range of applications such as a nitrating reagent and rocket 5-7

TNM becomes a highly sensitive and powerful explosive when contaminated

37

The computational description of photoinduced reactions is a great challenge and a

38

practical demand. Reduced density matrix (RDM) equation of motion allows analysis of

39

photoinduced relaxation of charge carriers for semiconductors.17-19 Nonadiabatic molecular

40

dynamics (NAMD) have been used to study photophysical processes, such as charge transfer,

41

and photochemical processes, such as photoisomerization and photodissociation, due to

42

nonadiabatic dynamics.12, 20-32 The photoluminescence yields of silicon nanocrystals have been

43

investigated through NAMD with a multireference treatment of the electronic structure.33 In a

44

recent study, the spin-restricted time-dependent excited-state molecule dynamics (TDESMD) 2 ACS Paragon Plus Environment

Page 2 of 22

Page 3 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

45

was used to simulate the photofragmentation of neutral lanthanide cyclopentadienyl complexes,

46

where the computed fragments show good agreement with fragments experimentally observed

47

by photoionization time-of-flight (PI-TOF) mass spectrometry.34-36 It should be noted that

48

TDESMD is interpreted as “molecular dynamics for time-dependent electronic configuration”.

49

This highlights the difference from ground state MD, fixed excited state MD, and nonadiabatic

50

MD.

51

Theoretical studies for systems with open-shell molecules have attracted much

52

attention.37-38 The fragment molecular orbital (FMO) theory based on fragmentation approach

53

has been used to perform MD simulations for open-shell systems.39-41 Grimme et al. studied the

54

decomposition of ionized molecules by MD simulations. The computed mass spectra extracted

55

from these simulations agreed with experimental electron impact mass spectra.42-43

56

When a gas-phase polyatomic molecule interacts with the laser field, it can undergo

57

multiphoton absorption such that so-called “ladder switching” or “ladder climbing” processes

58

take place.44-46 In the former case, the polyatomic molecule first dissociates and neural fragments

59

absorb additional photons to ionize, whereas in the latter case, the polyatomic molecule first

60

ionizes and the ion absorbs additional photons to dissociate. The two processes are in

61

competition. It is difficult to determine whether the “ladder switching” or “ladder climbing”

62

dominates.

63

In this work, TNM is used as a test model. The photofragmentation dynamics of closed-

64

shell neutral TNM and open-shell TNM+ are explored by a novel spin-unrestricted time-

65

dependent excited-state molecular dynamics (u-TDESMD) algorithm based on Rabi oscillations

66

and principles similar to trajectory surface hopping, with a mid-intensity field approximation. A

3 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 22

67

clear understanding of the photodissociation of this small compound is of critical importance to

68

the elucidation of the photochemical reactions involved in the case of more complex molecules. The procedure of spin-restricted TDESMD is described in detail in previous work.34-36, 47-

69 70

48

71

(β) components. As an approximation, the spin flip transitions are not considered, assuming

72

vanishing spin-orbit coupling. In the framework of u-TDESMD calculations, an ensemble

73

average provides results equivalent to a single trajectory, as rationalized below. Therefore, one

74

uses a single trajectory instead of an ensemble average. This feature of the methodology

75

originates from zero initial velocities of all ions at the initial time as an approximation. Even if

76

one waives this zero-velocity approximation, the amount of kinetic energy transferred to the

77

system from light does exceed initial kinetic energy of ions   = 0 ≪   ≫ 0. Thus, the

78

dependence on sampling of initial conditions is expected to vanish. In the following equations,

79

 the label = α or β is used to indicate spin. The Kohn-Sham orbitals , ,  , orbital

80

energies  ,  , and total density of electrons   can be obtained from the geometry

81

optimized model at initial time and from any updated geometry at later times according to

82

density functional theory (DFT) procedures.49 The density matrix elements  ,  serve as

83

weight coefficients for the total density of electrons

Here we use the spin-unrestricted method i.e. u-TDESMD to isolate spin up (α) and spin down

84

 ∗  ,  = ∑ ,  ,  , , .

85

The time evolution of electronic degrees of freedom can be calculated by solving the

86

equation of motion for the density operator ρ!" cast in terms of the Liouville−von Neumann

87

superoperator ℒ" and Redfield superoperator ℛ" ,

88

&



ρ! = ℏ )F+" , ρ!" , + . &' "

/ ,01 /

2

/033

= −ℒ" + ℛ" ρ!" .

4 ACS Paragon Plus Environment

(1)

(2)

Page 5 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

89

: ∙  , where 5+  represents ground state  Here Fock matrix reads F+" = 5+  + 6+ 78  − 9



90

: transition dipole operator,   =  0 ∙  Fock matrix, 6+ 78  nonadiabatic couplings, 9



91

cos? @ABC  electric field with ? @ABC /2F the laser field frequency.50-51 Application of rotating

92

wave approximation (RWA) in the interaction picture allows numerical propagation of equation

93

of motion using slowly changing time−dependent Hamiltonian Fock operators for exploring

94

coupled electronic and nuclear trajectory of long duration with acceptable precision.52 In this

95

 ∙ case, the light-to-matter interaction operator becomes time−independent, according to [9

96

 ,I ∙  0 . The electrons transitions 0 → 1 and 0 ← 1 are induced with the ] ,I ≈ 9

97

M@N M@N  ,I ∙  0, transition−specific Rabi frequency ? ,I /2F upon laser perturbation, ℏ? ,I =9

98

 ,I is the electric−dipole−moment matrix element in the independent orbital where 9

99

approximation (IOA).53 Propagation of electronic degrees of freedom (Eq. 2) is modeled as an

100

approximation of optically driven Rabi oscillations with instantaneous and discrete hops in the

101

elements of density matrix as an educated guess for solution. During a transition event, a

102

stepwise change in occupations of two participating orbitals 0 and 1 develops in time as then

103

introduced by, ∆Q

104

 , = 1 →  , = 0, ∆ , = −1

105

 ,II = 0 →  ,II = 1, ∆ ,II = +1.

(3a)

∆Q

RST,UV

106

Electronic dissipative transitions .

107

78  are computed along nuclear molecular dynamics trajectory. Nonadiabatic couplings 6 ,I

108

trajectory

 

RQ

according

2

(3b)

RAA

are facilitated by nuclear motions computed along

to

the

on−the−fly

5 ACS Paragon Plus Environment

procedure

as,

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 22

ℏ

109

∗  ∗  78  = − X / [ , 6 ,I ,   ,I ,   + ∆ − ,I ,   , ,   + W∆Q

110

∆].54-56 The autocorrelation function 9 ,IY Z is processed by averaging along the duration

111

of the trajectory as, 9 ,IY Z = \ X] 6 ,I  + Z6 ,Y / . A Fourier transform of the

112

autocorrelation function provides elements of Redfield tensor, which control the dissipative

113

dynamics of the density matrix, .

114

78  ∙  _. calculations, the nonadiabatic coupling is negligible as 6 ,I < _9

[

\

RST,UV RQ

2

RAA

= ∑ ,  ,IY  , . Note that in u-TDESMD

115

The updated total density   + ∆ is then used in the Kohn−Sham self−consistent

116

procedure, and determines the energy gradient and forces 5 [] imposed on each nuclei of

117

the model, R`

118

RQ `

  = 5 []/9 .

(4)

119

Coupled electronic and nuclear degrees of freedom are propagated forward in time using Eq.1

120

for feedback.

121

In u-TDESMD algorithm, the leading order process is represented by the molecule

122

undergoing cyclic excitations and de-excitations. During excitation cycles, the nuclear kinetic

123

energy is accumulated to overcome the dissociation barrier. Time of elementary reaction event is

124

determined by observing bond distance over time / and comparing it with a threshold value

125

/′. In the case of bond breaking or bond formation events at the instant of time ′, |/′ − /′| >

126

, where  is the tolerance.57-59 The u-TDESMD trajectory generates “hot” intermediates with

127

nonzero kinetic energy. It is difficult to calculate the activation energy of dissociation reaction

128

because of uncertainty in total energies of “hot” intermediates. Therefore, an attempt to identify

129

high precision activation energy has been committed based on artificial removal of kinetic 6 ACS Paragon Plus Environment

Page 7 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

130

energy component. One uses a post-processing technique referred to as “cooling” to extract the

131

intermediates with no influence of kinetic energy from the trajectory. A single point energy

132

calculation is applied to “hot” intermediates. Thus, the kinetic energy does not contribute to the

133

barrier height. It should be noted that the post-processing treatment does not affect u-TDESMD

134

simulations, because the “cool” intermediates don’t enter into the trajectory. Along the u-

135

TDESMD trajectory of coordinates and momenta, the energy and forces are evaluated at each

136

QhQ  = time step as a function of both nuclear positions d e and momenta df e as ghQ

137

 QhQ [d e, df e] . However, the “cooling” concept is based on artificial resetting of

138

QhQ  =  QhQ [d e, df  ≡ 0e]. momenta to zero value as ihh

139

The u-TDESMD algorithm describes the dissociation of polyatomic molecules or ions

140

under intermediate laser field. Photoionization mass spectra can be extracted from u-TDESMD

141

trajectories with certain approximations. (i) Intensities of features in the mass spectra are

142

determined by the number of corresponding fragments in the trajectory. (ii) A post-dissociation

143

ionization process, as a sampling method, is assumed rather than modeled for all fragments. Each

144

fragment is treated with a single positive charge. (iii) The distribution of features in the mass

145

spectra is determined by a finite−width Lorentzian function, where the center is located at the

146

molecule weight of corresponding fragments and the width is set as 0.1.

147

In the simulation cell, a 9 Å vacuum in each direction, x, y, z, is added to minimize

148

interactions between the fragments and penetrations into the simulation cell, mimicking low

149

pressure gas or vacuum environment. Calculations are done in a basis set of Kohn−Sham (KS)

150

orbitals computed in DFT using the Perdew−Burke−Ernzerhof (PBE) form of generalized

151

gradient approximation (GGA) with the projected augmented wave (PAW) potentials as

152

implemented in the Vienna Ab initio Simulation Package (VASP).60-64 Starting from the 7 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

153

optimized geometry, u-TDESMD calculations were performed for 600 fs using a time step of 1

154

fs with an inverse Rabi frequency of 10 fs. Atomics models were visualized using VESTA

155

software.65

156

Figure 1 shows the basic electronic structure of neutral TNM and TNM+ computed by

157

PBE functional. For the neutral TNM the density of states (DOS) (Figure 1a) and calculated

158

absorption spectra (Figure 1b) of spin α and spin β components are identical, since it is in

159

closed-shell system with spin paired electrons. The calculated band gaps are k,l = k,m = 3.23

160

eV. In contrast, the DOS (Figure 1c) and calculated absorption spectra (Figure 1d) of TNM+ are

161

different for spin α and spin β components. The calculated band gaps are k,l = 3.28 and

162

k,m = 0.20 eV.

163

There are several features in the calculated absorption spectra. The electronic transitions

164

with the leading contribution to these features are summarized in Table 1 and are explored in u-

165

TDESMD to simulate the photodissociation reaction. In the case of neutral TNM, we only

166

consider the spin α component to save computational resources. One would expect that

167

trajectories induced by spin α and spin β transitions are identical because of indistinguishable

168

electronic structures. In the case of open-shell TNM+, both spin α and spin β components are

169

considered. In addition, there are several features in the range between 0 and 2 eV for the

170

calculated absorption spectrum of TNM+ of spin β component. These features might contribute

171

to the photofragmentation of the open-shell system. However, they are not explored in u-

172

TDESMD simulations to make a consistent comparison study in terms of UV-Vis range of

173

excitation energy.

8 ACS Paragon Plus Environment

Page 8 of 22

Page 9 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

174

Figure 2 shows the energy diagram of intermediates in u-TDESMD trajectory with

175

electrons hopping between the orbital pair (HO–7, LU+3)α by using neutral TNM molecule as

176

the starting point. Note the calculated absorption spectrum changes during the trajectory such

177

that the most probable transition will involve different orbital pairs. At the moment, the orbital

178

pair [i(0), j(0)] is chosen based on the calculated absorption spectrum of the geometry optimized

179

initial reactant. In future, we plan to use time-dependent orbital pairs [i(t), j(t)] for u-TDESMD

180

calculations.

181

In Figure 2, the initial reactant and final product are geometry optimized. The single

182

point energy calculation is performed for “hot” intermediates generated in the trajectory to get

183

the total energy without kinetic energy of bond contraction and bond elongation. The first 500 fs

184

of the trajectory is characterized by the sequential elimination of the NO2 group. Bielski and

185

Timmons studied the photolysis of TNM at 77 K and found the primary pathway is a split into

186

NO2 and C(NO2)3.3 In our simulation, the ejection of NO2 is observed at 131 fs. The ejection of

187

another NO2 is observed at 216 fs. It should be noted that in this study dissociated fragments are

188

kept inside the simulation cell instead of being removed. Thus, the ejected fragments undergo

189

recombination and re-elimination in the subsequent trajectory. One can practically overcome this

190

“trapping artifact” by allowing the simulation cell to expand during the trajectory. Later on, a

191

local maximum of the total energy is found at 540 fs where ejected NO2 groups drift away from

192

the remaining C(NO2)2 fragment, as evidenced by the increase of C-N distance in the diagram.

193

The activation energy of Ea = 8.72 eV is obtained by subtraction of the total energy of

194

intermediate at 540 fs from the total energy of the reactant i.e. geometry optimized TNM

195

molecule. Subsequently, one observes the isomerization of C(NO2) fragment, if we take the other

196

bound NO2 group as a non-participating spectator. The isomerization reaction is essential for the 9 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 22

197

elimination of NO fragment. Other studies on the decomposition of the nitro-functionalized

198

compounds using different approaches also show the isomerization C(NO2) → C-O-N-O.12, 66-67

199

Finally, the spectator NO2 group is eliminated giving rise to CO, evidenced by the decrease of C-

200

O distance in the diagram. The product is composed of CO, NO, and 3 NO2 gases. The total

201

energy difference between the final product and the initial reactant is about ∆E = 1.08 eV. In this

202

work, the u-TDESMD simulations were performed for a short period of time. In such cases, the

203

system probably doesn’t accumulate enough kinetic energy to overcome the dissociation barrier

204

to reach the global minima. However, the final product from the simulation agrees with

205

experimental results.8 Bock and Zanathy studied the pyrolysis of gas-phase TNM and found the

206

compound decomposed completely into gaseous CO, NO, and 3 NO2 components over 580 K.8

207

The dissociation reactions in Figure 2 can be summarized in equations (5a) – (5d), gu

CNOW t vw CNOW x + NOW , ∆E = 2.66 eV

208 209 210 211

gu

CNOW x + NOW vw CNOW W + 2 NOW , ∆E = 1.97 eV gu

CNOW W + 2 NOW vw OCNOW + NO + 2 NOW , ∆E = 0.38 eV , E@ = 4.09 eV gu

OCNOW + NO + 2 NOW vw CO + NO + 3 NOW , ∆E = −3.93 eV

(5a) (5b) (5c) (5d)

212

where ∆E is the total energy difference between the product and reactant for each reaction and Ea

213

is the activation energy.

214

The energy diagram of intermediates in u-TDESMD trajectory with electrons hopping

215

between the orbital pair (HO–2, LU+6)α and (HO–6, LU+4)β by using TNM+ as the starting point

216

can be found in Figure S1 and S2 in the supporting information, respectively. In both cases, the

217

major dissociation pathway is still the elimination of NO2 group. The isomerization of C(NO2) is

218

again observed and leads to the formation of CO by the elimination of NO. It is found that the

10 ACS Paragon Plus Environment

Page 11 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

219

cation is much easier to dissociate than the neutral species. In Figure S1, the activation energy

220

(Ea), energy difference between final product and initial reactant (∆E), and the time scale of the

221

dissociation reaction are about 3.35 eV, -1.96 eV, and 300 fs, respectively. In Figure S2, the

222

corresponding values are about 4.65 eV, -2.04 eV, and 500 fs, respectively. Later increases in

223

energy can be interpreted as an artifact of the finite cell size, and collisions of the products. The

224

CO, NO, and NO2 yield of each trajectory can be found in Table 1.

225

We also calculate the total energies of reactant, transition state i.e. intermediate with the

226

highest total energy, and product of Figure 2, S1 and S2 using DFT method with

227

Heyd−Scuseria−Ernzerhof (HSE06)68-69 functional implemented in VASP and time-dependent

228

DFT (TDDFT)70 method with Becke, 3-parameter, Lee-Yang-Parr (B3LYP)71 functional

229

implemented in Gaussian72, see Figure 3. One observes that Ea and ∆E vary with different

230

functionals. Figure 3 suggests the dissociation reaction starting with the cation is exothermic,

231

whereas the one starting with the neutral is endothermic.

232

Figure 4a-4c show simulated mass spectra based on u-TDESMD trajectories. As a

233

reference, the experimental electron ionization (EI) mass spectrum73 is shown in Figure 4d. The

234

dominant feature is NO2+ for all mass spectra. Features such as C(NO2)3+ and C(NO2)2+ are

235

present in both simulated and experiment mass spectra, even though the relative intensities are

236

different. Some distinct features such as CO+ are only found in the simulated mass spectra, while

237

CN+ and CNO+ are only observed in the experiment EI mass spectrum. It should be pointed out

238

that the feature corresponding to the molecular ion is strong in the simulated mass spectrum

239

based on the simulation starting with neutral TNM. However, it is weak in the simulated mass

240

spectra based on simulations starting with TNM+.

241

fragment than the neutral, as the ionization makes the bond length longer and thus weakening the

It confirms that the cation is easier to

11 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 22

242

bonding. The molecular ion is not observed in the experimental EI mass spectrum. This is not

243

surprising considering the high-energy electron impact creates high-energy molecular ion that

244

subsequently dissociates.

245

In summary, a recently developed u-TDESMD algorithm taking into account spin

246

configurations has been used to model the photodissociation of TNM. Both the closed-shell

247

neutral TNM and open-shell TNM+ have been used as starting points for simulations. It is found

248

that the cation is easier to dissociate than the neutral species in terms of shorter reaction time and

249

lower activation energy. The major dissociation pathway is the ejection of NO2. The final

250

products in certain trajectories are completely composed of gas-phase CO, NO, and 3 NO2

251

components. These observations agree well with experimental findings.3,

252

present simulations show that the isomerization of C(NO2) fragment is a necessary step for the

253

formation of CO and NO. The ab initio mass spectra are extracted from u-TDESMD trajectories

254

with certain approximations. The interpretation of computational results provides insights about

255

reaction mechanisms and product distributions that are not available in photofragmentation

256

experiments. The u-TDESMD methodology has the potential to model and monitor

257

photoreactions with open-shell intermediates and radicals.

258

Corresponding Author

259

*(D.S.K.) E−mail: [email protected]

8

In addition, the

260 261

Notes

262

The authors declare no competing financial interest.

263 264

Acknowledgments

265

This research was supported by NSF award EPS−0903804, CHE−1413614 for methods development and

266

by DOE, BES −Chemical Sciences, NERSC Contract No. DE−AC02−05CH11231, allocation Award

12 ACS Paragon Plus Environment

Page 13 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

267

89959 “Computational Modeling of Photocatalysis and Photoinduced Charge Transfer Dynamics on

268

Surfaces”. DSK acknowledges support from NDSU Department of Chemistry and Biochemistry and

269

College of Science and Mathematics. BR gratefully acknowledges support from the North Dakota State

270

University Center for Computationally Assisted Science and Technology and the DOE Grant No.

271

DE−SC0001717, as well as support from NSF under ND EPSCoR Award #IIA-1355466 and by the State

272

of North Dakota.

273 274

Supporting Information Available: Energy diagrams of intermediates in u-TDESMD trajectory by

275

using TNM+ as the starting point.

13 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

276

References

277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320

1. Tschinkel, J. G., Tetranitromethane as Oxidizer in Rocket Propellants. Ind. Eng. Chem. 1956, 48 (4), 732-735. 2. Altukhov, K. V.; Perekalin, V. V., The Chemistry of Tetranitromethane. Russ. Chem. Rev. 1976, 45 (11), 1052-1066. 3. Bielski, B. H. J.; Timmons, R. B., Electron Paramagnetic Resonance Study of the Photolysis of Nitromethane, Methyl Nitrite, and Tetranitromethane at 77°K. J. Phys. Chem. 1964, 68 (2), 347-352. 4. Hager, K. F., Tetranitromethane. Ind. Eng. Chem. 1949, 41 (10), 2168-2172. 5. Abello, N.; Kerstjens, H. A. M.; Postma, D. S.; Bischoff, R., Protein Tyrosine Nitration: Selectivity, Physicochemical and Biological Consequences, Denitration, and Proteomics Methods for the Identification of Tyrosine-Nitrated Proteins. J. Proteome Res. 2009, 8 (7), 3222-3238. 6. Sokolovsky, M.; Riordan, J. F.; Vallee, B. L., Tetranitromethane. A Reagent for the Nitration of Tyrosyl Residues in Proteins. Biochemistry 1966, 5 (11), 3582-3589. 7. Jaworska-Augustyniak, A.; Wojtczak, J., The Explosive Reaction of Tetranitromethane with Ferrocene. J. Transition Met. Chem. 1979, 4 (3), 207-208. 8. Bock, H.; Zanathy, L., The Pyrolysis of Tetranitromethane in the Gas Phase. Angew. Chem., Int. Ed. Engl. 1992, 31 (7), 900-902. 9. Frank, A. J.; Grätzel, M.; Henglein, A., The 347.2 nm Laser Photolysis of Tetranitromethane in Polar, Nonpolar, and Micellar Solutions. Ber. Bunsenges. Phys. Chem. 1976, 80 (7), 593-602. 10. Asmus, K. D.; Chaudhri, S. A.; Nazhat, N. B.; Schmidt, W. F., Pulse Radiolysis Studies of Solutions of Tetranitromethane in Iso-Propanol. Trans. Faraday Soc. 1971, 67 (0), 2607-2617. 11. Fileti, E. E.; Chaban, V. V.; Prezhdo, O. V., Exploding Nitromethane in Silico, in Real Time. J. Phys. Chem. Lett. 2014, 5 (19), 3415-3420. 12. Nelson, T.; Bjorgaard, J.; Greenfield, M.; Bolme, C.; Brown, K.; McGrane, S.; Scharff, R. J.; Tretiak, S., Ultrafast Photodissociation Dynamics of Nitromethane. J. Phys. Chem. A 2016, 120 (4), 519-526. 13. Larentzos, J. P.; Rice, B. M., Transferable Reactive Force Fields: Extensions of ReaxFF-lg to Nitromethane. J. Phys. Chem. A 2017, 121 (9), 2001-2013. 14. Lee, J. H.; Kim, J. C.; Jeon, W. C.; Cho, S. G.; Kwak, S. K., Explosion Study of Nitromethane Confined in Carbon Nanotube Nanocontainer via Reactive Molecular Dynamics. J. Phys. Chem. C 2017, 121 (12), 6415-6423. 15. Citroni, M.; Bini, R.; Pagliai, M.; Cardini, G.; Schettino, V., Nitromethane Decomposition under High Static Pressure. J. Phys. Chem. B 2010, 114 (29), 9420-9428. 16. Dey, A.; Fernando, R.; Abeysekera, C.; Homayoon, Z.; Bowman, J. M.; Suits, A. G., Photodissociation Dynamics of Nitromethane and Methyl Nitrite by Infrared Multiphoton Dissociation Imaging with Quasiclassical Trajectory Calculations: Signatures of the Roaming Pathway. J. Chem. Phys. 2014, 140 (5), 054305. 17. Vazhappilly, T.; Hembree, R. H.; Micha, D. A., Photoconductivities from Band States and A Dissipative Electron Dynamics: Si(111) without and with Adsorbed Ag Clusters. J. Chem. Phys. 2016, 144 (2), 024107. 18. Han, Y.; Tretiak, S.; Kilin, D., Dynamics of Charge Transfer at Au/Si Metal-Semiconductor NanoInterface. Mol. Phys. 2014, 112 (3-4), 474-484. 19. Han, Y.; Micha, D. A.; Kilin, D. S., Ab initio Study of the Photocurrent at the Au/Si Metal– Semiconductor Nanointerface. Mol. Phys. 2015, 113 (3-4), 327-335. 20. Petersen, J.; Mitrić, R.; Bonačić-Koutecký, V.; Wolf, J.-P.; Roslund, J.; Rabitz, H., How Shaped Light Discriminates Nearly Identical Biochromophores. Phys. Rev. Lett. 2010, 105 (7), 073003.

14 ACS Paragon Plus Environment

Page 14 of 22

Page 15 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367

The Journal of Physical Chemistry Letters

21. Snyder, J. W.; Curchod, B. F. E.; Martínez, T. J., GPU-Accelerated State-Averaged Complete Active Space Self-Consistent Field Interfaced with Ab Initio Multiple Spawning Unravels the Photodynamics of Provitamin D3. J. Phys. Chem. Lett. 2016, 7 (13), 2444-2449. 22. Subotnik, J. E.; Alguire, E. C.; Ou, Q.; Landry, B. R.; Fatehi, S., The Requisite Electronic Structure Theory To Describe Photoexcited Nonadiabatic Dynamics: Nonadiabatic Derivative Couplings and Diabatic Electronic Couplings. Acc. Chem. Res. 2015, 48 (5), 1340-1350. 23. Fazzi, D.; Barbatti, M.; Thiel, W., Unveiling the Role of Hot Charge-Transfer States in Molecular Aggregates via Nonadiabatic Dynamics. J. Am. Chem. Soc. 2016, 138 (13), 4502-4511. 24. Nguyen, T. S.; Parkhill, J., Nonradiative Relaxation in Real-Time Electronic Dynamics OSCF2: Organolead Triiodide Perovskite. J. Phys. Chem. A 2016, 120 (34), 6880-6887. 25. Muuronen, M.; Parker, S. M.; Berardo, E.; Le, A.; Zwijnenburg, M. A.; Furche, F., Mechanism of Photocatalytic Water Oxidation on Small TiO2 Nanoparticles. Chem. Sci. 2017. 26. Greenfield, M. T.; McGrane, S. D.; Bolme, C. A.; Bjorgaard, J. A.; Nelson, T. R.; Tretiak, S.; Scharff, R. J., Photoactive High Explosives: Linear and Nonlinear Photochemistry of Petrin Tetrazine Chloride. J. Phys. Chem. A 2015, 119 (20), 4846-4855. 27. Chaban, V. V.; Pal, S.; Prezhdo, O. V., Laser-Induced Explosion of Nitrated Carbon Nanotubes: Nonadiabatic and Reactive Molecular Dynamics Simulations. J. Am. Chem. Soc. 2016, 138 (49), 1592715934. 28. Neukirch, J. A.; Jinhee, P.; Vladmir, Z.; Hong, W.; Pavel, J.; Oleg, V. P.; Hong-Cai, Z.; James, P. L., Calculated Photo-Isomerization Efficiencies of Functionalized Azobenzene Derivatives in Solar Energy Materials: Azo-Functional Organic Linkers for Porous Coordinated Polymers. J. Phys.: Condens. Matter 2015, 27 (13), 134208. 29. Nelson, T.; Naumov, A.; Fernandez-Alberti, S.; Tretiak, S., Nonadiabatic Excited-State Molecular Dynamics: On-the-fly Limiting of Essential Excited States. Chem. Phys. 2016, 481, 84-90. 30. Shu, Y.; Levine, B. G., First-Principles Study of Nonradiative Recombination in Silicon Nanocrystals: The Role of Surface Silanol. J. Phys. Chem. C 2016, 120 (40), 23246-23253. 31. Vincent, J. C.; Muuronen, M.; Pearce, K. C.; Mohanam, L. N.; Tapavicza, E.; Furche, F., That Little Extra Kick: Nonadiabatic Effects in Acetaldehyde Photodissociation. J. Phys. Chem. Lett. 2016, 7 (20), 4185-4190. 32. Li, X.; Tully, J. C.; Schlegel, H. B.; Frisch, M. J., Ab initio Ehrenfest dynamics. J. Chem. Phys. 2005, 123 (8), 084106. 33. Shu, Y.; Kortshagen, U. R.; Levine, B. G.; Anthony, R. J., Surface Structure and Silicon Nanocrystal Photoluminescence: The Role of Hypervalent Silyl Groups. J. Phys. Chem. C 2015, 119 (47), 26683-26691. 34. Chen, J.; Hochstatter, A. M.; Kilin, D.; May, P. S.; Meng, Q.; Berry, M. T., Photofragmentation of Gas-Phase Lanthanide Cyclopentadienyl Complexes: Experimental and Time-Dependent Excited-State Molecular Dynamics. Organometallics 2014, 33 (7), 1574-1586. 35. Han, Y.; Kilin, D. S.; May, P. S.; Berry, M. T.; Meng, Q., Photofragmentation Pathways for GasPhase Lanthanide Tris(isopropylcyclopentadienyl) Complexes. Organometallics 2016, 35 (20), 3461-3473. 36. Han, Y.; Meng, Q.; Rasulev, B.; May, P. S.; Berry, M. T.; Kilin, D. S., Photofragmentation of the Gas-Phase Lanthanum Isopropylcyclopentadienyl Complex: Computational Modeling vs Experiment. J. Phys. Chem. A 2015, 119 (44), 10838-10848. 37. Isayev, O.; Gorb, L.; Zilberberg, I.; Leszczynski, J., Electronic Structure and Bonding of {Fe(PhNO2)}6 Complexes:  A Density Functional Theory Study. J. Phys. Chem. A 2007, 111 (18), 3571-3576. 38. Jensen, S. J.; Inerbaev, T. M.; Kilin, D. S., Spin Unrestricted Excited State Relaxation Study of Vanadium(IV)-Doped Anatase. J. Phys. Chem. C 2016, 120 (11), 5890-5905. 39. Green, M. C.; Nakata, H.; Fedorov, D. G.; Slipchenko, L. V., Radical Damage in Lipids Investigated with the Fragment Molecular Orbital Method. Chem. Phys. Lett. 2016, 651, 56-61.

15 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414

Page 16 of 22

40. Nakata, H.; Schmidt, M. W.; Fedorov, D. G.; Kitaura, K.; Nakamura, S.; Gordon, M. S., Efficient Molecular Dynamics Simulations of Multiple Radical Center Systems Based on the Fragment Molecular Orbital Method. J. Phys. Chem. A 2014, 118 (41), 9762-9771. 41. Pruitt, S. R.; Nakata, H.; Nagata, T.; Mayes, M.; Alexeev, Y.; Fletcher, G.; Fedorov, D. G.; Kitaura, K.; Gordon, M. S., Importance of Three-Body Interactions in Molecular Dynamics Simulations of Water Demonstrated with the Fragment Molecular Orbital Method. J. Chem. Theory Comput. 2016, 12 (4), 1423-1435. 42. Grimme, S., Towards First Principles Calculation of Electron Impact Mass Spectra of Molecules. Angew. Chem., Int. Ed. 2013, 52 (24), 6306-6312. 43. Bauer, C. A.; Grimme, S., How to Compute Electron Ionization Mass Spectra from First Principles. J. Phys. Chem. A 2016, 120 (21), 3755-3766. 44. Levis, R. J.; DeWitt, M. J., Photoexcitation, Ionization, and Dissociation of Molecules Using Intense Near-Infrared Radiation of Femtosecond Duration. J. Phys. Chem. A 1999, 103 (33), 6493-6507. 45. Ledingham, K. W. D.; Singhal, R. P.; Smith, D. J.; McCanny, T.; Graham, P.; Kilic, H. S.; Peng, W. X.; Wang, S. L.; Langley, A. J.; Taday, P. F.; et al., Behavior of Polyatomic Molecules in Intense Infrared Laser Beams. J. Phys. Chem. A 1998, 102 (18), 3002-3005. 46. Sharma, P.; Vatsa, R. K.; Maity, D. K.; Kulshreshtha, S. K., Laser Induced Photodissociation of CH2Cl2 and CH2Br2 at 355 nm: An Experimental and Theoretical Study. Chem. Phys. Lett. 2003, 382 (5–6), 637-643. 47. Chen, J.; Meng, Q.; Stanley May, P.; Berry, M. T.; Kilin, D. S., Time-Dependent Excited-State Molecular Dynamics of Photodissociation of Lanthanide Complexes for Laser-Assisted Metal-Organic Chemical Vapour Deposition. Mol. Phys. 2014, 112 (3-4), 508-517. 48. Disrud, B.; Han, Y.; Kilin, D. S., Molecular Dynamics of Laser-Assisted Decomposition of Unstable Molecules at the Surface of Carbon Nanotubes: Case Study of CH2(NO2)2 on CNT(4,0). Mol. Phys. 2017, 115 (5), 674-682. 49. Kohn, W.; Sham, L. J., Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140 (4A), A1133-A1138. 50. Rabi, I. I.; Ramsey, N. F.; Schwinger, J., Use of Rotating Coordinates in Magnetic Resonance Problems. Rev. Mod. Phys. 1954, 26 (2), 167-171. 51. Rabi, I. I., Space Quantization in a Gyrating Magnetic Field. Phys. Rev. 1937, 51 (8), 652-654. 52. Micha, D. A.; Santana, A., Dissipative Quantum Dynamics with Many Coupled Molecular States:  Photodesorption from Metal Surfaces. J. Phys. Chem. A 2003, 107 (37), 7311-7317. 53. Kilina, S.; Kilin, D.; Tretiak, S., Light-Driven and Phonon-Assisted Dynamics in Organic and Semiconductor Nanostructures. Chem. Rev. 2015, 115 (12), 5929-5978. 54. Goyal, P.; Schwerdtfeger, C. A.; Soudackov, A. V.; Hammes-Schiffer, S., Nonadiabatic Dynamics of Photoinduced Proton-Coupled Electron Transfer in a Solvated Phenol–Amine Complex. J. Phys. Chem. B 2015, 119 (6), 2758-2768. 55. Auer, B.; Soudackov, A. V.; Hammes-Schiffer, S., Nonadiabatic Dynamics of Photoinduced Proton-Coupled Electron Transfer: Comparison of Explicit and Implicit Solvent Simulations. J. Phys. Chem. B 2012, 116 (26), 7695-7708. 56. Hammes-Schiffer, S.; Tully, J. C., Proton Transfer in Solution: Molecular Dynamics with Quantum Transitions. J. Chem. Phys. 1994, 101 (6), 4657-4667. 57. O'Boyle, N. M.; Banck, M.; James, C. A.; Morley, C.; Vandermeersch, T.; Hutchison, G. R., Open Babel: An Open Chemical Toolbox. J. Cheminf. 2011, 3, 33. 58. Meng, Q.; May, P. S.; Berry, M. T.; Kilin, D., Sequential Hydrogen Dissociation from A Charged Pt13H24 Cluster Modeled by Ab initio Molecular Dynamics. Int. J. Quantum Chem. 2012, 112 (24), 38963903.

16 ACS Paragon Plus Environment

Page 17 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448

The Journal of Physical Chemistry Letters

59. Sapp, W.; Gifford, B.; Wang, Z.; Kilin, D. S., Mathematical Modeling of Gas Desorption from a Metal-Organic Supercontainer Cavity Filled with Stored N2 Gas at Critical Limits. RSC Adv. 2017, 7 (18), 11180-11190. 60. Perdew, J. P.; Burke, K.; Ernzerhof, M., Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77 (18), 3865-3868. 61. Hohenberg, P.; Kohn, W., Inhomogeneous Electron Gas. Phys. Rev. 1964, 136 (3B), B864-B871. 62. Kresse, G.; Hafner, J., Ab initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47 (1), 558-561. 63. Kresse, G.; Hafner, J., Ab initio Molecular-Dynamics Simulation of the Liquid-Metal–AmorphousSemiconductor Transition in Germanium. Phys. Rev. B 1994, 49 (20), 14251-14269. 64. Kresse, G.; Furthmüller, J., Efficiency of ab-initio Total Energy Calculations for Metals and Semiconductors Using a Plane-Wave Basis Set. Comput. Mater. Sci. 1996, 6 (1), 15-50. 65. Momma, K.; Izumi, F., VESTA 3 for Three-Dimensional Visualization of Crystal, Volumetric and Morphology Data. J. Appl. Crystallogr. 2011, 44 (6), 1272-1276. 66. Chaban, V. V.; Fileti, E. E.; Prezhdo, O. V., Buckybomb: Reactive Molecular Dynamics Simulation. J. Phys. Chem. Lett. 2015, 6 (5), 913-917. 67. Chaban, V. V.; Prezhdo, O. V., Energy Storage in Cubane Derivatives and Their Real-Time Decomposition: Computational Molecular Dynamics and Thermodynamics. ACS Energy Lett. 2016, 1 (1), 189-194. 68. Heyd, J.; Scuseria, G. E.; Ernzerhof, M., Hybrid Functionals Based On A Screened Coulomb Potential. J. Chem. Phys. 2003, 118 (18), 8207-8215. 69. Heyd, J.; Scuseria, G. E.; Ernzerhof, M., Erratum: “Hybrid Functionals Based on A Screened Coulomb Potential” [J. Chem. Phys. 118, 8207 (2003)]. J. Chem. Phys. 2006, 124 (21), 219906. 70. Runge, E.; Gross, E. K. U., Density-Functional Theory for Time-Dependent Systems. phys. Rev. Lett. 1984, 52 (12), 997-1000. 71. Stephens, P. J.; Devlin, F. J.; Chabalowski, C. F.; Frisch, M. J., Ab Initio Calculation of Vibrational Absorption and Circular Dichroism Spectra Using Density Functional Force Fields. J. Phys. Chem. 1994, 98 (45), 11623-11627. 72. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G. A.; et al., Gaussian 09, revision B.01. Gaussian, Inc.: Wallingford, CT, 2010. 73. NIST Mass Spec Data Center, S.E. Stein, director, "Mass Spectra" in NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, Gaithersburg MD, 20899, doi:10.18434/T4D303, (retrieved June 8, 2017).

449 450

17 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

(a)

(b) B C

D E F

Absorption (a.u.)

A

Density of states

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 22

(c)

(d)

d

f g

e a b c a' b'

e'

c'

f' g'

d' -2

0

2

4

6

8

0

2

4

h' 6

8

Transition energy, eV

Orbital energy, eV 451 452

Figure 1. (a, c) Spin-polarized density of states for TNM and TNM+, respectively. The filled area

453

represents occupied states whereas the unfilled area represents unoccupied states. (b, d) Calculated

454

absorption spectra (dashes) for TNM and TNM+, respectively. The solid vertical sticks indicate the

455

electronic transitions of the most contribution with the height equal to the oscillator strength. In each

456

panel the upper curve indicates spin α component and the lower indicates spin β component.

457

18 ACS Paragon Plus Environment

Page 19 of 22

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

458 459

Figure 2. Energy diagram of intermediates extracted from u-TDESMD simulation with electrons hopping

460

between the orbital pair (HO–7, LU+3)α by using TNM as the starting point. The initial reactant and final

461

product are geometry optimized. The single point energy calculation is performed for intermediate atomic

462

models to get the total energy without kinetic energy of bond contraction and bond elongation. The red

463

solid, blue short dashes, green long dashes represent total energy, average C-N distance, and C-O distance

464

for selected atoms. This diagram illustrates activation energies for several steps of ultrafast cracking

465

reactions.

466

19 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 22

467 468

Figure 3. Energy diagram of three important points extracted from Figure 2, S1, and S2 and computed by

469

different functional upon single point energy calculations. In each case, the left and right lines indicate the

470

initial reactant and final product, respectively. The middle line represents the intermediate with the

471

highest total energy. Total energies are shown with respect to the total energy of reactant for each curve.

472

The red, blue, and green codes indicate results at the level of DFT/PBE, DFT/HSE06, and

473

TDDFT/B3LYP, respectively.

474 475

20 ACS Paragon Plus Environment

N+ O+

C(NO2 )4+

C(NO2 )3+

CNO 2+ / OCNO +

(b)

C(NO2 )2 +

CO + NO+

OCNO 2+

(a)

Intensity (a.u.)

(c)

0

476

CNO +

(d) CN+

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry Letters

NO2 +

Page 21 of 22

50

100

150

200

m/z

477

Figure 4. Simulated mass spectra from u-TDESMD trajectories with electrons hopping between (a)

478

orbitals pair (HO–7, LU+3)α by using TNM as the starting point, (b) orbitals pair (HO–2, LU+6)α, and (c)

479

orbitals pair (HO–6, LU+4)β by using TNM+ as the starting point. (d) The experimental electron

480

ionization mass spectrum of TNM.

481

21 ACS Paragon Plus Environment

The Journal of Physical Chemistry Letters

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

482 483

Page 22 of 22

Table 1. Electronic transitions contributing to u-TDESMD simulations and theoretical yields of photofragments feature (Figure 1) A B C D E F a b c d e f g a' b' c' d' e' f' g' h'

transition energy (eV) 3.39 4.52 4.94 7.52 8.15 8.50 3.43 3.90 4.35 4.62 4.99 7.98 8.45 3.23 3.75 4.31 4.54 6.20 7.72 7.44 8.23

oscillator strength 0.019 0.077 0.045 0.067 0.067 0.065 0.023 0.018 0.045 0.090 0.048 0.082 0.064 0.025 0.022 0.045 0.135 0.057 0.100 0.065 0.079

orbital pair (HO-3, LU)α (HO-7, LU+3)α (HO-10, LU+2)α (HO-1, LU+4)α (HO-5, LU+4)α (HO-2, LU+7)α (HO-2, LU)α (HO-4, LU)α (HO-9, LU)α (HO-7, LU+3)α (HO-10, LU+1)α (HO-2, LU+4)α (HO-2, LU+6)α (HO-1, LU+1)β (HO-4, LU+1)β (HO-8, LU+1)β (HO-6, LU+4)β (HO-17, LU)β (HO-1, LU+5)β (HO-20, LU)β (HO-4, LU+5)β

484

22 ACS Paragon Plus Environment

NO2 0.24 0.12 0.23 0.25 0.03 0.10 0.17 0.11 0.12 0.23 0.28 0.57 0.16 0.14 0.08 0.33 0.01 0.42 0.19

fragment yield NO CO 0.02 0.03 0.03 0.03 0.06 0.24 0.61 0.06 0.21 0.13 0.32 0.06 -