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目录 contents

    摘要

    为探明外电场中炸药感度的变化规律,借助B3LYP/6⁃311++G(2d,p)和M06⁃2X/6⁃311++G(2d,p)理论方法,研究了外电场方向和强度的变化对1,4⁃二硝基咪唑⁃N⁃氧化物(1,4⁃DNIO)炸药潜在引发键的键长、硝基电荷、键离解能及撞击感度、静电火花感度和冲击起爆压力的影响。结果表明,在无电场和外电场作用下,N─NO2是最可能的引发键,其次是NO,最后是C─NO2键。沿NO、C─NO2键轴正方向和N─NO2负方向的外电场使NO和C─NO2键离解能减小、N─NO2键离解能增大、H50增大、撞击感度降低;与上述反方向的外电场对引发键强度和撞击感度的影响正好相反。引发键键长、AIM电子密度、硝基电荷、键离解能和H50的变化量分别与外电场强度之间呈良好的线性关系,大多数情况下,相关系数R2 ˃ 0.9500。外电场对电火花感度和冲击起爆压力的影响不大,外电场由-0.010 a.u.变化到0.010 a.u.,变化值分别小于0.5 J和0.15 MPa。

    Abstract

    In order to explore the variation rule of explosives′ sensitivity in the external electric field, the bond lengths, nitro charges, bond dissociation energies of the potential trigger linkages and the impact sensitivities, electrostatic spark sensitivities as well as shock initiation pressures of the 1,4⁃dinitroimidazole⁃N⁃oxide (1,4⁃DNIO) explosive were investigated by the B3LYP/6⁃311++G(2d,p) and M06⁃2X/6⁃311++G(2d,p) levels of theory. Results show that the N─NO2 bond is the most likely trigger linkage in the initiation reaction of explosive, followed by N→O, and finally the C─NO2 bond in the external electric fields and the absence of the electric fields. Under the external electric fields along the positive directions of the N→O and C─NO2 bond axes as well as the negative direction of the N─NO2 bond axis, the dissociation energies of the N→O and C─NO2 bonds are decreased, while those of N─NO2 bond are increased, leading to the increases of the H50 values and thus the decreases of the impact sensitivities. The opposite conclusion is drawn when the explosives are in the external electric fields with the reverse directions against the above cases. The changes in the bond lengths (ΔR), electron density values (Δρ), nitro charges (ΔQ), bond dissociation energy (ΔBDEs) of the trigger linkages and thoes in the impact sensitivities (ΔH50) show good linear relationships withthe external electric field strengths, respectively. In most cases, the values of correlation coefficient R2 are larger than 0.9500. The external electric fields have little effect on the electrostatic spark sensitivities or shock initiation pressures, accompanied by the variations lower than 0.5 J and 0.15MPa with the field strengths from –0.0010 a.u. to 0.0010 a.u., respectively.

    Graphic Abstract

    图文摘要

    In order to introduce the external electric fields into the explosive systems safely and effectively, the bond lengths, nitro charges, bond dissociation energies of the potential trigger linkages and the impact sensitivities, electrostatic spark sensitivities as well as shock initiation pressures of 1,4⁃dinitroimidazole⁃N⁃oxide were investigated by the B3LYP/6⁃311++G(2d,p) and M06⁃2X/6⁃311++G(2d,p) levels of theory. The essence of the high sensitivity was revealed by means of the resonance theory of the aromatic ring structure.

  • 1 引 言

    外电场可提高炸药爆轰波阵面附近气体能量、增大炸药爆速和爆[1,2],而且其在炸药体系中的应用已受到了人们的青[3]。然而,炸药在制备、加工、运输、储存和使用过程中可能发生电场事故的安全问题,导致目前向炸药体系引入外电场的许多关键技术仍难以突[4,5]。为了探明外电场中炸药感度的变化规律,将外电场安全有效地引入炸药体系,近年来人们对外电场中炸药感度的研究工作展开了从实验到理论、宏观到微观、热力学到动力学全方位的探[5,6,7,8]。例如,俄罗斯科学家Rodzevich[5]借助实验方法研究了外电场对叠氮化银分解速率的影响。Politzer[9,10,11]和宋晓[12]等采用密度泛函理论(DFT)方法研究了几种单质炸药分子在电场中的偶极矩、引发键伸缩振动频率和静电势等的变化趋势。杨明理[13,14]借助DFT方法讨论了外电场对CH3NO2和1,1⁃二氨基⁃2,2⁃二硝基乙烯 (FOX⁃7) 引发键C—NO2断裂反应的影响。近年来,任福德等借助DFT⁃B3LYP和MP2方法比较了外电场对CH3NO2和NH2NO2[15]、2,4,6⁃三硝基甲苯(TNT)和黑索今(RDX)[16]分子中的C/N─NO2、C/N─H键和硝基中N─O键强度的影响,探讨了外电场中奥克托今(HMX)/FOX⁃7共晶体系结合能的变[17]及CH3NO2的分解反应动力[7,8]

    对于存在多个化学键强度相差不大的潜在引发键的炸药分子,外电场方向和强度的改变可能导致引发键类型的改[6,7,8,15]。探明外电场对该类炸药分子潜在引发键强度和类型的影响,对于正确预测其在外电场中的感度是必要的。

    N→O配位键是炸药潜在的引发键之[18]。理论研究表[19],硝基咪唑环3⁃位氮原子形成N→O配位键的N⁃氧化物爆轰性能可优于六硝基六氮杂异伍兹烷(CL⁃20)。为此,本研究选择1,4⁃二硝基咪唑⁃N⁃氧化物 (1,4⁃DNIO)为目标物质,探讨外电场方向和强度对N→O、N─NO2、C─NO2和C─H键强度影响,确定外电场中的引发键,预测撞击感度、静电火花感度和冲击起爆压力随外电场方向和强度改变的变化规律,以期为将外电场引入含有N→O配位键分子的含能材料体系而避免偶然爆炸的技术提供理论指导。

  • 2 计算方法

    所有计算均采用Gaussian 09 程序[20]完成。借助B3LYP/6⁃311++G(2d,p)和M06⁃2X/6⁃311++G(2d,p)理论方法进行了分子的结构优化和AIM(atoms in molecules)[21]、Mulliken电荷、APT(atomic polar tensors)电荷、前线轨道、分子表面静电[22]分析以及撞击感度、静电火花感度和冲击起爆压力的预测。

    由于垂直于引发键方向的外电场对引发键强度的影响不显[15],本研究仅选择了平行于N→O、N─NO2和C─NO2潜在引发键方向的外电场,电场强度分别为±0.002,±0.004,±0.006,±0.008,±0.010 a.u.(表1)。电场的正方向规定从给电子体指向吸电子体的方向为正方向。因此,对于N→O、N─NO2和C─NO2的电场方向,正方向分别是指由N原子指向O、N和C指向硝基N原子(图1)。

    Table 1 Selected bond lengths(R), AIM electron densities(ρ), Mulliken and APT nitro charges (Q) of 1,4⁃DNIO with different external electric field strengths and orientations at the B3LYP/6⁃311++G(2d,p) (in flat) and M06⁃2X/6⁃311++G(2d,p) (in bold) levels

    fieldRN(3)ORN(1)NRC(4)─NρN(3)‒O/a.u.ρN(1)─N/a.u.ρC(4)─N/a.u.QNO2a/eQNO2b/a.u.
    no field1.25931.42821.43950.49690.35080.2725-0.2297(0.4337)-0.2437(0.0664)
    1.25651.41091.44030.50280.35250.2678-0.2121(0.4263)-0.2341(0.0332)
    +0.010(N(3)O)1.29551.41251.44480.48390.36060.2631-0.2349(0.4302)-0.2415(0.0685)
    1.28781.39571.44510.48830.36410.2561-0.2172(0.4248)-0.2317(0.0352)
    +0.008(N(3)O)1.28491.41611.44280.48610.35820.2635-0.2343(0.4307)-0.2418(0.0681)
    1.27861.39811.44360.49150.36030.2583-0.2158(0.4242)-0.2326(0.0341)
    +0.004(N(3)O)1.26821.42221.44130.49100.35350.2682-0.2313(0.4325)-0.2432(0.0668)
    1.26401.40381.44190.49720.35610.2638-0.2137(0.4262)-0.2338(0.0333)
    -0.004(N(3)O)1.25371.43451.43840.50050.34670.2723-0.2282(0.4342)-0.2443(0.0660)
    1.25201.41581.43910.50670.34850.2683-0.2115(0.4270)-0.2345(0.0327)
    -0.008(N(3)O)1.24891.43571.43600.50620.34290.2763-0.2262(0.4362)-0.2460(0.0652)
    1.24711.41831.43690.51170.34410.2722-0.2101(0.4275)-0.2363(0.0316)
    -0.010(N(3)O)1.24531.43931.43510.50880.33840.2790-0.2231(0.4379)-0.2482(0.0649)
    1.24371.42061.43580.51410.34050.2749-0.2090(0.4283)-0.2375(0.0310)
    +0.010(N(1)─N)1.25181.47081.43500.50650.33750.2841-0.2270(0.4382)-0.2468(0.0638)
    1.24971.46171.43650.51150.33810.2773-0.2085(0.4310)-0.2379(0.0305)
    +0.008(N(1)─N)1.25401.45191.43680.50380.34100.2790-0.2277(0.4367)-0.2462(0.0644)
    1.25151.43151.43770.50920.34280.2731-0.2092(0.4299)-0.2368(0.0316)
    +0.004(N(1)─N)1.25681.43531.43850.50050.34720.2752-0.2291(0.4346)-0.2444(0.0660)
    1.25421.41751.43920.50590.34910.2704-0.2115(0.4275)-0.2351(0.0327)
    -0.004(N(1)─N)1.26191.41761.43990.49380.35360.2715-0.2305(0.4330)-0.2430(0.0669)
    1.25901.40081.44170.50010.35510.2663-0.2128(0.4266)-0.2332(0.0338)
    -0.008(N(1)─N)1.26431.40681.44180.48920.35610.2663-0.2335(0.4317)-0.2411(0.0682)
    1.26181.38921.44350.49530.35790.2622-0.2157(0.4252)-0.2315(0.0354)
    -0.010(N(1)─N)1.26571.40211.44420.48650.35830.2641-0.2346(0.4308)-0.2398(0.0699)
    1.26351.38371.44570.49290.35970.2618-0.2160(0.4244)-0.2300(0.0356)
    +0.010(C(4)─N)1.27521.42211.44460.48790.36130.2603-0.2335(0.4297)-0.2401(0.0705)
    1.27031.40411.44520.49190.36160.2547-0.2147(0.4222)-0.2302(0.0368)
    +0.008(C(4)─N)1.27121.42331.44330.49010.35790.2628-0.2319(0.4308)-0.2412(0.0694)
    1.26761.40521.44430.49420.35920.2572-0.2133(0.4238)-0.2313(0.0359)
    +0.004(C(4)─N)1.26561.42531.44160.49390.35370.2689-0.2297(0.4323)-0.2430(0.0672)
    1.26281.40731.44170.49830.35510.2637-0.2116(0.4263)-0.2335(0.0339)
    -0.004(C(4)─N)1.25481.43291.43810.50330.34560.2752-0.2293(0.4344)-0.2446(0.0652)
    1.25191.41451.43870.50480.35050.2699-0.2112(0.4268)-0.2351(0.0328)
    -0.008(C(4)─N)1.24931.43751.43590.50830.34100.2797-0.2280(0.4356)-0.2485(0.0634)
    1.24751.41911.43610.50910.34490.2747-0.2096(0.4281)-0.2366(0.0317)
    -0.010(C(4)─N)1.24581.43861.43380.51160.33910.2830-0.2271(0.4365)-0.2488(0.0629)
    1.24461.42351.43400.51270.34180.2789-0.2092(0.4286)-0.2379(0.0311)

    NOTE: aMulliken and APT(in parentheses) charges of the —NO2 group involving the N—NO2 moiety. b)Mulliken and APT charges of the —NO2 group involving the C—NO2 moiety.

    图1
                            1,4⁃DNIO的结构及外电场方向

    图1 1,4⁃DNIO的结构及外电场方向

    Fig. 1 Structure and external electric field directions for 1,4⁃DNIO

  • 3 结果与讨论

  • 3.1 结构和硝基电荷

    炸药感度与引发键的强度、硝基电荷密切相[23]。为探明外电场中炸药感度的变化规律,首先探讨了外电场方向和强度对1,4⁃DNIO潜在引发键强度和硝基电荷的影响。

    表1给出了1,4⁃DNIO在电场中的键长、AIM电子密度、Mulliken和APT硝基电荷的理论计算值。可以看出,在两种理论水平上计算得到的键长和AIM电子密度值均接近。在外电场作用下,N(3)O和N(1)─N键长变化较大,C(4)─N次之,C(2)─H键长几乎没变;与外电场方向平行的化学键键长受电场的影响较显著:沿N(3)O和C(4)─N(即C─NO2) 键轴正方向的外电场拉长了N(3)O和C(4)─N键长,缩短了N(1)─N (即N─NO2)键长;沿N(1)─N键轴正方向的外电场缩短了N(3)O和C(4)─N键长,拉长了N(1)─N键长;沿N(3)O、C(4)─N和N(1)─N负方向外电场的键长变化分别与其正方向外电场结果相反;键长改变量(与无电场的键长值之差,ΔR)与外电场强度 (E) 之间存在良好的线性关系(图2),这与本课题组之前对CH3NO2和NH2NO2在外电场中的计算结果一[15]

    图2
                            键长变化量(ΔR)、AIM电子密度变化量(Δρ)、硝基电荷变化值(ΔQ)、键离解能变化值(ΔBDE)与外电场强度(E)之间的线性关系

    图2 键长变化量(ΔR)、AIM电子密度变化量(Δρ)、硝基电荷变化值(ΔQ)、键离解能变化值(ΔBDE)与外电场强度(E)之间的线性关系

    Fig. 2 Changes in the bond lengths (ΔR), electron densities (Δρ), nitro charges (ΔQ), bond dissociation energy (ΔBDE) versus field strengths (E) in different fields

    表1 在B3LYP/6⁃311++G(2d,p)(平滑)和M06⁃2X/6⁃311++G(2d,p)(黑体)水平上计算得到的1,4⁃DNIO在不同电场大小和方向的部分键长,AIM电子密度,Mulliken和APT 硝基电荷

    在两种理论计算水平上,在外电场作用下,AIM电子密度变化的强度与趋势几乎与之相应的化学键键长变化一致,且其改变量(与无电场的电子密度之差,Δρ)与外电场强度(E)之间也存在良好的线性关系(图2)。根据AIM理[21],化学键临界点的电子密度越大,化学键强度越强,键长越短; 反之,电子密度越小,化学键强度越弱,键长越长; 而且,电子密度改变越大,键长的变化越显著。此即为外电场中键长变化的本质原因。比较发现,1,4⁃DNIO中引发键键长和电子密度的变化量及其与外电场强度之间呈线性关系的相关系数R2值均大于CH3NO2和NH2NO2在外电场中相应的计算结[15]。这可能是由于具有1218结构的1,4⁃DNIO中的π电子在外电场中较CH3NO2和NH2NO2σ电子更易移动造成的。

    大多数情况下,在两种理论计算水平上,沿N(3)O和C(4)─N键轴正方向的外电场使N─NO2的硝基Mulliken电荷值(绝对值)增大、APT电荷值减小,而使C─NO2的硝基Mulliken电荷值减小、APT电荷值增大; 沿N(1)─N键轴正方向的外电场使N─NO2的硝基Mulliken电荷值减小、APT电荷值增大,而使C─NO2的硝基Mulliken电荷值增大、APT电荷值减小;负方向外电场中,硝基的Mulliken和APT值的变化分别与其正方向外电场结果相反;N─NO2的硝基电荷变化趋势总与C─NO2相反,导致外电场中1,4⁃DNIO分子的偶极矩变大。硝基电荷的改变量(ΔQ) 与外电场强度(E)之间呈良好的线性关系(图2)。

  • 3.2 引发键离解能

    炸药引发键离解能与感度密切相[24,25]。因此,本研究探讨了1,4⁃DNIO在外电场中潜在引发键离解能的变化(表2),其中,对于RO键的离解能,采用三重态氧进行计算。

    Table 2 Bond dissociation energy (E), statistical quantities of surface electrostatic potentials (σ+2,σ-2), electric spark sensitivities (EES), impact sensitivities (H50) and shock initiation pressures (lnp) of 1,4⁃DNIO with different external electric field strengths and orientations at the B3LYP/6⁃311++G(2d,p) (in flat) and M06⁃2X/6⁃311++G(2d,p) (in bold) levels

    field

    BDEN(3)O

    /kJ∙mol-1

    BDEN(1)─N

    /kJ∙mol-1

    BDEC(4)─N

    /kJ∙mol-1

    ELUMO

    /a.u.

    σ+2

    /kcal·mol-1

    σ-2

    /kcal·mol-1

    EES

    /J

    H50

    /cm

    lnp

    /MPa

    No field205.854.7301.1-0.15384308.478.32.30486.78
    189.185.0396.7-0.10739285.369.62.07366.88
    +0.010(N(3)O)171.272.8278.1-0.17982352.980.12.38686.84
    158.899.3373.5-0.12639337.873.92.14516.93
    +0.008(N(3)O)184.166.2285.3-0.16718337.086.82.36626.82
    165.394.5381.0-0.12017318.675.22.12456.91
    +0.004(N(3)O)196.558.3294.5-0.15872317.282.32.32556.79
    180.587.8390.1-0.11236293.874.62.09406.89
    -0.004(N(3)O)213.753.5307.5-0.15858302.575.32.29446.77
    196.883.6404.1-0.11379283.666.62.07336.87
    -0.008(N(3)O)226.852.0318.2-0.16713312.368.02.27326.77
    212.381.8415.3-0.12360280.659.52.06296.86
    -0.010(N(3)O)235.851.5325.2-0.17138298.162.42.25206.76
    227.979.3420.8-0.12289273.657.32.05276.86
    +0.010(N(1)─N)229.543.5322.3-0.16336291.668.82.28356.74
    217.870.2421.7-0.11931276.555.62.04176.82
    +0.008(N(1)─N)222.848.1316.9-0.16297290.171.92.28396.75
    208.277.6417.2-0.11558278.461.82.05256.85
    +0.004(N(1)─N)211.952.7306.2-0.15427299.676.52.29466.77
    196.583.0403.3-0.10956283.766.22.06316.87
    -0.004(N(1)─N)200.157.8295.0-0.15621311.582.32.31536.79
    184.589.2388.1-0.11169288.674.72.08446.89
    -0.008(N1─N)189.966.8281.3-0.16137313.789.82.34656.82
    171.597.2372.7-0.11898298.180.52.12526.92
    -0.010(N(1)─N)180.275.7273.5-0.16670319.995.62.36746.85
    163.7104.0360.9-0.12373306.783.22.12556.94
    +0.010(C(4)─N)182.566.6272.3-0.16577326.592.22.35686.82
    167.393.7366.7-0.11826322.381.52.11516.91
    +0.008(C(4)─N)189.762.5280.2-0.16125325.288.62.33626.80
    175.989.1376.5-0.11463302.776.02.09456.89
    +0.004(C(4)─N)200.056.1293.7-0.15753318.383.52.30556.78
    185.285.9389.6-0.10992289.872.32.07406.88
    -0.004(C(4)─N)209.753.7306.5-0.15927298.775.22.30446.77
    196.084.6404.8-0.11123276.566.82.06336.87
    -0.008(C(4)─N)220.550.6318.9-0.16808288.566.52.29326.76
    210.279.3417.2-0.12021265.063.92.06296.86
    -0.010(C(4)─N)227.945.1328.5-0.17152283.158.12.29206.74
    218.372.6429.1-0.12536261.862.02.06276.83

    大多数情况下,在两种理论计算水平上,随着外电场强度的改变,与电场方向平行的引发键离解能变化较明显;沿N(3)O和C(4)─N键轴正方向的外电场使N(3)O和C(4)─N键离解能减小、使N(1)─N键离解能增大;沿N(1)─N键轴正方向的外电场增大了N(3)O和C(4)─N键离解能、减弱了N(1)─N键离解能;负方向外电场中的键离解能的变化分别与其正方向外电场变化相反。在外电场作用下,N(3)O和N(1)─N键离解能变化较大,C(4)─N次之,C(2)─H键离解能几乎没有变化。这些结果均佐证了外电场中引发键键长和AIM电子密度的计算结果。键离解能的变化量(ΔBDE)与外电场强度(E)之间存在良好的线性关系(图2)。

    在两种理论水平上的计算结果均表明,在无电场和外电场作用下,1,4⁃DNIO中引发键的离解能均遵循以下顺序:BDEN(1)─N<<BDEN(3)→O<BDEC(4)─N<<BDEC(2)─H。这表明,1,4⁃DNIO起爆反应中N(1)─NO2键首先断裂,其次是N(3)→O,C(4)─NO2和C(2)─H键不易断裂。因此,在无电场和外电场作用下,1,4⁃DNIO最可能的引发键为N(1)─NO2键,其次是N(3)→O键,C(4)─NO2和C(2)─H成为引发键的可能性较小。

    在无电场和外电场作用下,1,4⁃DNIO中N─NO2引发键离解能小于100.0 kJ∙mol-1(除沿N(1)─N负方向且强度为0.010 a.u.的电场外)。一般地,非芳香环上的N─NO2键离解能接近200.0 kJ∙mol-1 [26]。为解释1,4⁃DNIO芳香环上N─NO2离解能小的原因,进行了其环中心NICS (nucleus⁃independent chemical shift) (NICS(0,π))[27]计算。一般地,NICS(0,π)值越大,单双键共振程度和芳香性越强,分子或自由基越稳定。在M06⁃2X/6⁃311++G(2d,p)水平上,沿N(1)—N键轴方向电场强度从-0.010 a.u.变化到0.010 a.u.(步长为0.002 a.u.),由1,4⁃DNIO的N─NO2键均裂生成的4⁃硝基咪唑⁃N⁃氧化物自由基的NICS(0,π)值分别为-4.82、-4.76、-4.75、-4.75、-4.74、-4.74、-4.74、-4.74、-4.73、-4.73、-4.72。这些值均接近配位O在1⁃位氮原子上的4⁃硝基咪唑⁃N⁃氧化物自由基相应值(最大差别不足0.05)。这表明,4⁃硝基咪唑⁃N⁃氧化物自由基的1⁃位和3⁃位不仅存在较强的互变共振模式,而且二者的稳定性相当,与实验结果吻[28,29]。众所周知,1⁃位氮原子上含有取代基的咪唑自由基非常稳定,因此N(1)─NO2键均裂生成的4⁃硝基咪唑氧自由基较稳定。由键离解能定义式可知,均裂自由基产物越稳定,键离解能越小。这可能是1,4⁃DNIO中N─NO2引发键离解能小的根源。由此可预测,1,4⁃DNIO不稳定,感度较高。

    表2 在B3LYP/6⁃311++G(2d,p) (平滑)和M06⁃2X/6⁃311++G(2d,p) (黑体)水平上计算的1,4⁃DNIO在不同电场大小和方向的部分键离解能(E)、表面静电势统计量(σ+2,σ-2)、静电火花感度(EES)、撞击感度(H50)和冲击起爆压力(lnp)

  • 3.3 撞击感度、静电火花感度和冲击起爆感度

    根据Murray[30]的建议,硝胺炸药的撞击感度H50可按式(1)估算:

    H50=0.8849[σ+2σ-2σ+2-σ-2]-34.03[σ-2σ+2]2-43.15
    (1)

    式中,σ+2σ-2分别表示表面静电势的正、负方差。

    计算结果见表2。Murry[30]根据式(1)计算得到的无外电场存在下的RDX撞击感度H50值为26 cm,本研究在M06⁃2X/6⁃311++G(2d,p)水平上计算的RDX和1,4⁃DNIO 的H50值分别为28 cm和48 cm。可见,1,4⁃DNIO的撞击感度低于RDX。H50值受外电场强度的影响较大:沿N(3)O和C(4)─N键轴正方向和N(1)─N键轴负方向的外电场使H50值增大,撞击感度降低;反之,沿N(3)O和C(4)─N键轴负方向和N(1)─N键轴正方向的外电场使H50值变小,撞击感度升高。该计算结果与N─NO2在外电场中的引发键强度变化趋势一致,这也证实了N─NO2是引发键。外电场中H50值的变化量(ΔH50)与外电场强度(E)之间存在良好的线性关系(图3)。

    图3
                            撞击感度变化值(ΔH50)与外电场强度(E)之间的线性关系

    图3 撞击感度变化值(ΔH50)与外电场强度(E)之间的线性关系

    Fig. 3 Changes in impact sensitivity values (ΔH50) versus field strengths (E) in different field orientations

    根据文献[31],借助式(2)计算了1,4⁃DNIO在外电场中的静电火花感度EES

    EES=(-1)n110.16Qnitro-1.05n1n2ELUMO-0.20
    (2)

    式中,n1n2分别表示芳香环和取代基的个数,本研究中均取1;Qnitro为N─NO2引发键的Mulliken硝基电荷;ELUMO为分子前线分子轨道最低空轨道能量。

    在B3LYP/6⁃311G(d,p)理论水平上计算的1,4⁃DNIO的EES值为3.66 J,比TNT炸药[31],表明1,4⁃DNIO比TNT更敏感。与宋晓[12]等计算结果类似,外电场对电火花感度影响不大。外电场由-0.010 a.u.变化到0.010 a.u.,静电火花感度的变化值不足0.5 J。

    冲击起爆压力可用来评价冲击波感度的大小。根据Tan[25],冲击起爆压力用式(3)计算:

    lnp=6.84×104BDE+0.532Qnitro-1.28×10-2BDEQnitro+2.09
    (3)

    式中,BDE和Qnitro分别取N─NO2引发键的键离解能和Mulliken硝基电荷。

    表2可知,1,4⁃DNIO在外电场作用下的冲击起爆压力与季戊四醇四硝酸酯(PETN)(实验值:6.62 MPa[25])接近,而小于HMX(实验值:6.99 MPa和RDX(实验值:7.01 MPa)[25]。因而,1,4⁃DNIO的冲击波感度接近PETN,而高于HMX和RDX。与静电火花感度类似,外电场对1,4⁃DNIO冲击起爆压力的影响不大。外电场由-0.010 a.u.变化到0.010 a.u.,冲击起爆压力的变化值低于0.15 MPa。

    可以推测,将外电场引入含有N→O配位键分子的含能材料体系,应考虑外电场对炸药撞击感度的影响,可忽略其对静电火花感度和冲击波感度的影响。需要说明的是,本研究中计算得到的外电场中静电火花感度和冲击起爆压力的值是在没考虑外电场与静电场、冲击波耦合作用下的结果。考虑耦合作用下的电火花感度和冲击波感度的理论研究可能成为将来研究的重点,因为耦合是不可避免的。

    总之,沿N→O、C─NO2键轴正方向和N─NO2负方向的外电场使N→O和C─NO2键离解能减小、N─NO2键离解能增大、H50值增大、撞击感度降低;与上述反方向的外电场使N→O和C─NO2键离解能增大、N─NO2键离解能减小、H50值减小、撞击感度升高。在外电场作用下,电子在分子(特别是在引发键)的重新分配使分子偶极矩和引发键上成键电子密度发生较大变化,导致引发键离解能和分子的稳定性发生较大变化,引起炸药撞击感度的变化(仅分子水平上)。不同取向的外电场导致电子在分子的重新分配趋势有差异(正负方向外电场引起的结果可能正好相反),从而引起不同的感度变化趋势。

  • 4 结 论

    (1)在无电场和外电场作用下,1,4⁃DNIO中引发键的离解能均遵循以下顺序:BDEN(1)─N << BDEN(3)→O<BDEC(4)─N<<BDEC(2)─H,因而N—NO2是最可能的引发键,其次是NO,最后是C─NO2键。

    (2)外电场对N─NO2、NO、和C─NO2键强度影响较大,对C─H键性质的影响甚微。引发键键长、AIM电子密度、硝基电荷、键离解能和H50值的变化量与外电场强度之间存在良好的线性关系。

    (3)外电场对炸药撞击感度有较大影响,而对电火花感度和冲击起爆压力的度影响不大。可以推测,将外电场引入含有N→O配位键分子的含能材料体系,应考虑外电场对炸药撞击感度的影响,可忽视其对静电火花感度和冲击波感度的影响。

    (责编: 张 琪)

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      Schleyer PvR, Maerker C, Dransfeld A, et al. Nucleus⁃independent chemical shifts:  A simple and efficient aromaticity probe[J]. Journal of the American Chemical Society, 1996, 118: 6317-6318.

    • 28

      Bracuti A J, Molecular structure of a new potential propellant oxidize4,5⁃dinitroimdazole[J]. Journal of Chemical Crystallography,1996, 28(5): 367-371.

    • 29

      Wang J, Dong H, Zhang X Y, et al. Synthesis, Thermal stability and sensitivity of 2,4⁃dinitroimdazole[J]. Chinese Journal of Energetic Materials, 2010, 18(6): 728-729.

    • 30

      Murry J S, Lane P, Politzer P. Effects of strongly electron⁃attracting components on molecular surface electrostatic potentials application to predicting impact sensitivities of energetic molecules[J]. Molecular Physics, 1998, 93(2): 187-194.

    • 31

      Zhi C, Cheng X. The correlation between electric spark sensitivity of polynitroaromatic compounds and their molecular electronic properties[J]. Propellants Explosives Pyrotechnics, 2010, 35: 555-560.

王勇

机 构:中北大学化学工程与技术学院,山西 太原 030051

Affiliation:School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China

邮 箱:wangyong19890424@163.com

作者简介:王勇(1989-),女,博士,主要从事含能材料分子设计研究。e⁃mail:wangyong19890424@163.com

任福德

机 构:中北大学化学工程与技术学院,山西 太原 030051

Affiliation:School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China

角 色:通讯作者

Role:Corresponding author

邮 箱:fdren888@126.com

作者简介:任福德(1973-),男,高级实验师,主要从事含能材料分子设计与合成研究。e⁃mail:fdren888@126.com

曹端林

机 构:中北大学化学工程与技术学院,山西 太原 030051

Affiliation:School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China

袁军

机 构:中北大学朔州校区,山西 朔州036000

Affiliation:North university of China, Shuozhou, Shuozhou 036000, China

李永祥

机 构:中北大学化学工程与技术学院,山西 太原 030051

Affiliation:School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China

王建龙

机 构:中北大学化学工程与技术学院,山西 太原 030051

Affiliation:School of Chemical Engineering and Technology, North University of China, Taiyuan 030051, China

fieldRN(3)ORN(1)NRC(4)─NρN(3)‒O/a.u.ρN(1)─N/a.u.ρC(4)─N/a.u.QNO2a/eQNO2b/a.u.
no field1.25931.42821.43950.49690.35080.2725-0.2297(0.4337)-0.2437(0.0664)
1.25651.41091.44030.50280.35250.2678-0.2121(0.4263)-0.2341(0.0332)
+0.010(N(3)O)1.29551.41251.44480.48390.36060.2631-0.2349(0.4302)-0.2415(0.0685)
1.28781.39571.44510.48830.36410.2561-0.2172(0.4248)-0.2317(0.0352)
+0.008(N(3)O)1.28491.41611.44280.48610.35820.2635-0.2343(0.4307)-0.2418(0.0681)
1.27861.39811.44360.49150.36030.2583-0.2158(0.4242)-0.2326(0.0341)
+0.004(N(3)O)1.26821.42221.44130.49100.35350.2682-0.2313(0.4325)-0.2432(0.0668)
1.26401.40381.44190.49720.35610.2638-0.2137(0.4262)-0.2338(0.0333)
-0.004(N(3)O)1.25371.43451.43840.50050.34670.2723-0.2282(0.4342)-0.2443(0.0660)
1.25201.41581.43910.50670.34850.2683-0.2115(0.4270)-0.2345(0.0327)
-0.008(N(3)O)1.24891.43571.43600.50620.34290.2763-0.2262(0.4362)-0.2460(0.0652)
1.24711.41831.43690.51170.34410.2722-0.2101(0.4275)-0.2363(0.0316)
-0.010(N(3)O)1.24531.43931.43510.50880.33840.2790-0.2231(0.4379)-0.2482(0.0649)
1.24371.42061.43580.51410.34050.2749-0.2090(0.4283)-0.2375(0.0310)
+0.010(N(1)─N)1.25181.47081.43500.50650.33750.2841-0.2270(0.4382)-0.2468(0.0638)
1.24971.46171.43650.51150.33810.2773-0.2085(0.4310)-0.2379(0.0305)
+0.008(N(1)─N)1.25401.45191.43680.50380.34100.2790-0.2277(0.4367)-0.2462(0.0644)
1.25151.43151.43770.50920.34280.2731-0.2092(0.4299)-0.2368(0.0316)
+0.004(N(1)─N)1.25681.43531.43850.50050.34720.2752-0.2291(0.4346)-0.2444(0.0660)
1.25421.41751.43920.50590.34910.2704-0.2115(0.4275)-0.2351(0.0327)
-0.004(N(1)─N)1.26191.41761.43990.49380.35360.2715-0.2305(0.4330)-0.2430(0.0669)
1.25901.40081.44170.50010.35510.2663-0.2128(0.4266)-0.2332(0.0338)
-0.008(N(1)─N)1.26431.40681.44180.48920.35610.2663-0.2335(0.4317)-0.2411(0.0682)
1.26181.38921.44350.49530.35790.2622-0.2157(0.4252)-0.2315(0.0354)
-0.010(N(1)─N)1.26571.40211.44420.48650.35830.2641-0.2346(0.4308)-0.2398(0.0699)
1.26351.38371.44570.49290.35970.2618-0.2160(0.4244)-0.2300(0.0356)
+0.010(C(4)─N)1.27521.42211.44460.48790.36130.2603-0.2335(0.4297)-0.2401(0.0705)
1.27031.40411.44520.49190.36160.2547-0.2147(0.4222)-0.2302(0.0368)
+0.008(C(4)─N)1.27121.42331.44330.49010.35790.2628-0.2319(0.4308)-0.2412(0.0694)
1.26761.40521.44430.49420.35920.2572-0.2133(0.4238)-0.2313(0.0359)
+0.004(C(4)─N)1.26561.42531.44160.49390.35370.2689-0.2297(0.4323)-0.2430(0.0672)
1.26281.40731.44170.49830.35510.2637-0.2116(0.4263)-0.2335(0.0339)
-0.004(C(4)─N)1.25481.43291.43810.50330.34560.2752-0.2293(0.4344)-0.2446(0.0652)
1.25191.41451.43870.50480.35050.2699-0.2112(0.4268)-0.2351(0.0328)
-0.008(C(4)─N)1.24931.43751.43590.50830.34100.2797-0.2280(0.4356)-0.2485(0.0634)
1.24751.41911.43610.50910.34490.2747-0.2096(0.4281)-0.2366(0.0317)
-0.010(C(4)─N)1.24581.43861.43380.51160.33910.2830-0.2271(0.4365)-0.2488(0.0629)
1.24461.42351.43400.51270.34180.2789-0.2092(0.4286)-0.2379(0.0311)
html/hncl/CJEM2019082/media/09ef6609-ecdd-427f-817e-a81da0a9bc8f-image001.png
html/hncl/CJEM2019082/media/09ef6609-ecdd-427f-817e-a81da0a9bc8f-image002.png
field

BDEN(3)O

/kJ∙mol-1

BDEN(1)─N

/kJ∙mol-1

BDEC(4)─N

/kJ∙mol-1

ELUMO

/a.u.

σ+2

/kcal·mol-1

σ-2

/kcal·mol-1

EES

/J

H50

/cm

lnp

/MPa

No field205.854.7301.1-0.15384308.478.32.30486.78
189.185.0396.7-0.10739285.369.62.07366.88
+0.010(N(3)O)171.272.8278.1-0.17982352.980.12.38686.84
158.899.3373.5-0.12639337.873.92.14516.93
+0.008(N(3)O)184.166.2285.3-0.16718337.086.82.36626.82
165.394.5381.0-0.12017318.675.22.12456.91
+0.004(N(3)O)196.558.3294.5-0.15872317.282.32.32556.79
180.587.8390.1-0.11236293.874.62.09406.89
-0.004(N(3)O)213.753.5307.5-0.15858302.575.32.29446.77
196.883.6404.1-0.11379283.666.62.07336.87
-0.008(N(3)O)226.852.0318.2-0.16713312.368.02.27326.77
212.381.8415.3-0.12360280.659.52.06296.86
-0.010(N(3)O)235.851.5325.2-0.17138298.162.42.25206.76
227.979.3420.8-0.12289273.657.32.05276.86
+0.010(N(1)─N)229.543.5322.3-0.16336291.668.82.28356.74
217.870.2421.7-0.11931276.555.62.04176.82
+0.008(N(1)─N)222.848.1316.9-0.16297290.171.92.28396.75
208.277.6417.2-0.11558278.461.82.05256.85
+0.004(N(1)─N)211.952.7306.2-0.15427299.676.52.29466.77
196.583.0403.3-0.10956283.766.22.06316.87
-0.004(N(1)─N)200.157.8295.0-0.15621311.582.32.31536.79
184.589.2388.1-0.11169288.674.72.08446.89
-0.008(N1─N)189.966.8281.3-0.16137313.789.82.34656.82
171.597.2372.7-0.11898298.180.52.12526.92
-0.010(N(1)─N)180.275.7273.5-0.16670319.995.62.36746.85
163.7104.0360.9-0.12373306.783.22.12556.94
+0.010(C(4)─N)182.566.6272.3-0.16577326.592.22.35686.82
167.393.7366.7-0.11826322.381.52.11516.91
+0.008(C(4)─N)189.762.5280.2-0.16125325.288.62.33626.80
175.989.1376.5-0.11463302.776.02.09456.89
+0.004(C(4)─N)200.056.1293.7-0.15753318.383.52.30556.78
185.285.9389.6-0.10992289.872.32.07406.88
-0.004(C(4)─N)209.753.7306.5-0.15927298.775.22.30446.77
196.084.6404.8-0.11123276.566.82.06336.87
-0.008(C(4)─N)220.550.6318.9-0.16808288.566.52.29326.76
210.279.3417.2-0.12021265.063.92.06296.86
-0.010(C(4)─N)227.945.1328.5-0.17152283.158.12.29206.74
218.372.6429.1-0.12536261.862.02.06276.83
html/hncl/CJEM2019082/media/09ef6609-ecdd-427f-817e-a81da0a9bc8f-image003.png

Table 1 Selected bond lengths(R), AIM electron densities(ρ), Mulliken and APT nitro charges (Q) of 1,4⁃DNIO with different external electric field strengths and orientations at the B3LYP/6⁃311++G(2d,p) (in flat) and M06⁃2X/6⁃311++G(2d,p) (in bold) levels

图1 1,4⁃DNIO的结构及外电场方向

Fig. 1 Structure and external electric field directions for 1,4⁃DNIO

图2 键长变化量(ΔR)、AIM电子密度变化量(Δρ)、硝基电荷变化值(ΔQ)、键离解能变化值(ΔBDE)与外电场强度(E)之间的线性关系

Fig. 2 Changes in the bond lengths (ΔR), electron densities (Δρ), nitro charges (ΔQ), bond dissociation energy (ΔBDE) versus field strengths (E) in different fields

Table 2 Bond dissociation energy (E), statistical quantities of surface electrostatic potentials (σ+2,σ-2), electric spark sensitivities (EES), impact sensitivities (H50) and shock initiation pressures (lnp) of 1,4⁃DNIO with different external electric field strengths and orientations at the B3LYP/6⁃311++G(2d,p) (in flat) and M06⁃2X/6⁃311++G(2d,p) (in bold) levels

图3 撞击感度变化值(ΔH50)与外电场强度(E)之间的线性关系

Fig. 3 Changes in impact sensitivity values (ΔH50) versus field strengths (E) in different field orientations

image /

aMulliken and APT(in parentheses) charges of the —NO2 group involving the N—NO2 moiety. b)Mulliken and APT charges of the —NO2 group involving the C—NO2 moiety.

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      Murry J S, Lane P, Politzer P. Effects of strongly electron⁃attracting components on molecular surface electrostatic potentials application to predicting impact sensitivities of energetic molecules[J]. Molecular Physics, 1998, 93(2): 187-194.

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      Zhi C, Cheng X. The correlation between electric spark sensitivity of polynitroaromatic compounds and their molecular electronic properties[J]. Propellants Explosives Pyrotechnics, 2010, 35: 555-560.