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The kinetics of eighteen positive ions with chlorine azide (ClN3) have been studied using a selected ion flow tube (SIFT). These measurements allowed for the estimation of both the ionization energy, >930 kJ mol−1 (>9.6 eV), and the proton affinity, 713 ± 41 kJ mol−1, of chlorine azide. Reaction rate constants have been determined. Product ions have been identified, and quantified when synthetic complications allowed. In addition, general reaction trends have been observed. A reaction coordinate diagram for the novel reaction of N+ with ClN3 is discussed.

High-resolution synchrotron-radiation-based photoionization mass spectrometry was applied to study the dissociative photoionization of ClN 3 under collision-free molecular beam conditions at ionization energies between 10 and 17 eV. No parent ion (ClN 3 + ) could be detected under our experimental conditions. This suggests that the ground and excited states of ClN 3 + are weakly bound or repulsive, a conclusion supported by electronic structure calculations also reported here. We recorded photoionization yield spectra at m / z = 49, 42, 35 and 14 from which we extracted the appearance potentials for NCl + , N 3 + , Cl + , and N + . The appearance potential of NCl + (10.17 ± 0.02 eV) observed here is close to the previously reported ionization potential of ClN 3 obtained form photoelectron spectroscopy. Using the theoretically calculated binding energy of ClN 3 + (0.2 eV), we derive an estimate of the adiabatic ionization potential of ClN 3 = 9.97 ± 0.02 eV. The measured appearance potentials for N 3 + , Cl + , and N + provide three independent determinations of the Cl–N bond energy in ClN 3 , which agree within their respective error limits. The observations of this work are consistent with a new value of the N–Cl bond energy in ClN 3 , D 0 (Cl–N 3 ) = 1.86 ± 0.05 eV, 0.3 eV lower than previously reported values, which are however experimentally derived upper limits. The bond energy reported here is consistent with high level ab initio (CCSD(T)) electronic structure calculations extrapolated to the complete basis set limit, which yield a value: D 0 (Cl–N 3 ) = 1.87 eV.

The primary reaction products from 248-nm chlorine azide photolysis are identified in a collision-free experiment. In contrast to all previous reports, the radical channel producing Cl + N3 (95 � 3%) is seen to dominate the photochemistry. The molecular channel producing NCl + N2 (5 � 3%) was also observed. 2004 Elsevier B.V. All rights reserved.

The method of velocity map imaging was applied to study the photodissociation dynamics of ClN3 near 235 nm under collision-free conditions. Derived kinetic energy distributions of state-selected Cl (2PJ) provide a medium-resolution energy spectrum of the N3 fragment. Markedly bimodal distributions are observed that suggest simultaneous formation of the linear-N3 (X 2Π) isomer as well as an energetic form of N3, consistent with recent theoretical predictions of a cyclic isomer, resembling an isosceles triangle. Angular distributions of the photofragments indicate that 21A‘ ← 11A‘ excitation is the most important pathway to photoproducts. Branching ratio measurements between the dominant spin−orbit excited-state Cl* (2P1/2) and the spin−orbit ground-state Cl (2P3/2) showed Cl*/Cl ≈ 0.8/0.2. The branching ratio between linear-N3 and cyclic-N3 formation was determined to be ≈ 0.8/0.2.

A number of experiments have been performed in an effort to better understand the photoinitiated chain decomposition of ClN3. Discharge-flow methods were used to determine the rate of energy exchange between vibrationally excited N2 (a likely chain carrier) and ClN3. The rate constant for energy transfer from N2(v=1) to ClN3 was found to be (2.0 ± 1.0) × 10-13 cm3 s-1 at 300 K. This process is thought to excite the ν2 mode in ClN3 with the release of 281 cm-1 of excess energy. Experiments were also performed in which the decomposition of ClN3 was initiated by photolysis with a pulsed KrF laser at 249 nm, with subsequent observation of the time dependence of the densities of ClN3, electronically excited NCl(a1Δ), and vibrationally excited ClN3(ν2). A kinetic model for the ClN3 decomposition was assembled based on reactions with NCl(a1Δ) and N2(ν).

Kinetic measurements of NCl(a1Δ) metastables produced by the photolysis of chlorine azide (ClN3) at 193 nm are reported. High NCl(a1Δ) density (>1015 molecules/cm3) production facilitates measurements of the NCl(a1Δ) + NCl(a1Δ) self-annihilation rate. A gas phase transient chemical titration scheme is used to calibrate absolute NCl(a1Δ) density. The NCl(a1Δ) bimolecular rate coefficient at room temperature is (7.2 ± 0.9 × 10-12 cm3/(molecule s) and has a magnitude very critical to the development of an NCl(a1Δ) + I(2P3/2) → I*(2P1/2) + NCl(X3Σ-) chemical laser. Despite the large value of the self-annihilation rate, intense I*(2P1/2) emission via transfer from NCl(a1Δ) is strongly observed when mixtures of CH2I2 and ClN3 are photolyzed at 193 nm. Unlike the analogous O2(a1Δ) + I(2P3/2) energy transfer system, the relatively large NCl(a1Δ) bimolecular rate constant suggests that NCl(a1Δ) transport times must be short and will require small chemical mixing regions for efficient lasing. In addition, the 300 K...

International audience; We report the first time-resolved study of the photochemistry of chlorine azide (ClN3) by femtosecond velocity-map imaging (fs-VMI). The dissociation dynamics are initiated at 4.6 eV and the photofragments are detected by multiphoton ionization using an intense laser field centered at 803 nm. A dissociation time of 262 ± 38 fs was measured from the rising time of the co-fragments N3 and Cl. The time dependency of the angular distribution of N3, which converges from β2 ∼ 2 to β2 = 1.61 ± 0.07 in 170 ± 45 fs, reveals the parallel nature of the transition dipole moment.

The photodissociation dynamics of chlorine azide (ClN(3)) at the 157 nm region was studied theoretically using the multireference configuration interaction method and the complete active space self-consistent field direct dynamics method. The excitation at the 157 nm region was assigned to the 4 (1)A(')(S(7))--X (1)A(')(S(0)) transition. A likely pathway for the formation of cyclic N(3) after this transition was identified by direct dynamics as follows: ClN(3) excited to 4 (1)A(')(S(7)) dissociates after about 40 fs to excited N(3)(2 (2)A('), with about 44 kcal/mol internal energy) +Cl((2)P). This vibrationally hot N(3)(2 (2)A(')) goes diabatically through a conical intersection with N(3)(1 (2)A(')) at 44 fs onto 1 (2)A('). At 19 fs later and repeatedly after every 55 fs, N(3)(1 (2)A(')) crosses and trickles down via Coriolis coupling to N(3)(2 (2)A(")/ (2)B(1)) state, which has a potential minimum at the cyclic-N(3) structure. Some fraction of N(3)(2 (2)A(")/ (2)B(1)) produced will survive dissociation and will be found as the cyclic N(3), and some other fraction will eventually dissociate to N((2)D)+N(2) over a high barrier found previously.

Photofragment translational spectroscopy was used to identify the primary and secondary reaction pathways in 193 nm photodissociation of chlorine azide (ClN(3)) under collision-free conditions. Both the molecular elimination (NCl+N(2)) and the radical bond rupture channel (Cl+N(3)) were investigated and compared with earlier results at 248 nm. The radical channel strongly dominates, just as at 248 nm. At 193 nm, the ClN(3) (C (1)A(")) state is excited, rather than the B (1)A(') state that is accessed at 248 nm, resulting in different photofragment angular distributions. The chlorine translational energy distribution probing the dynamics of the radical bond rupture channel shows three distinct peaks, with the two fastest peaks occurring at the same translational energies as the two peaks seen at 248 nm that were previously assigned to linear and "high energy" N(3). Hence, nearly all the additional photon energy relative to 248 nm appears as N(3) internal excitation rather than as translational energy, resulting in considerably more spontaneous dissociation of N(3) to N(2)+N.

We report on an H(D)-atom Rydberg tagging experiment for H(D)N(3) photolysis providing detailed dynamical information on the wavelength dependence of the H(D) + N(3) channel. We observe subtle yet striking changes in the photochemical dynamics as the photolysis energy passes through approximately 5.6 eV. In addition to producing linear azide with an average of approximately 40% of available energy appearing as translation, a second H(D)-atom producing channel grows in above this energy releasing only about 15%. An observed (inverse) isotope effect suggests that statistical decomposition on S(0) is unimportant. High level ab initio quantum chemical calculations reveal a transition state to cyclization of the N(3) moiety in H(D)N(3) on the first excited singlet (S(1)) surface that is close in energy to the experimentally observed threshold energy for this "slow channel". Furthermore, the translational energy release of the "slow channel" is energetically consistent with cyclic-N(3) formation. This work provides the clearest presently available insights into how ring closure can occur in azide photochemistry.

Electron attachment to chlorine azide (ClN(3)) was studied using a flowing-afterglow Langmuir-probe apparatus. Electron attachment rates were measured to be 3.5x10(-8) and 4.5x10(-8) cm(3) s(-1) at 298 and 400 K, respectively, with an estimated 35% absolute accuracy. Cl(-) was the sole ion product of the attachment reaction; weak ion signals were observed for other anions and attributed to impurities and secondary ion-molecule reactions. Assuming a relative uncertainty of +/-10% for these data, an activation energy for the attachment reaction may be given as 24+/-10 meV.

Photofragmentation translational spectroscopy was used to identify the primary and secondary reaction pathways in the KrF laser (248 nm) photodissociation of chlorine azide (ClN(3)) under collision-free conditions. Both the molecular channel producing NCl (X (3)Sigma,a (1)Delta) + N(2) and the radical channel producing Cl ((2)P(J)) + N(3) were analyzed in detail. Consistent with previously reported velocity map ion imaging experiments [N. Hansen and A. M. Wodtke, J. Phys. Chem. A 107, 10608 (2003)] a bimodal translational energy distribution is seen when Cl atoms are monitored at mz = 35(Cl(+)). Momentum-matched N(3) counterfragments can be seen at mz = 42(N(3) (+)). The characteristics of the observed radical-channel data reflect the formation of linear azide radical and another high-energy form of N(3) (HEF-N(3)) that exhibits many of the characteristics one would expect from cyclic N(3). HEF-N(3) can be directly detected by electron-impact ionization more than 100 mus after its formation. Products of the unimolecular dissociation of HEF-N(3) are observed in the mz = 14(N(+)) and mz = 28(N(2) (+)) data. Anisotropy parameters were determined for the primary channels to be beta = -0.3 for the NCl forming channel and beta = 1.7 and beta = 0.4 for the linear N(3) and HEF-N(3) forming channels, respectively. There is additional evidence for secondary photodissociation of N(3) and of NCl.

Experiments directed toward elucidating the nature of fragments produced by the photodissociation of ClN3 have been performed. The utlraviolet absorption spectrum of this molecule exhibits three features between 300 and 170 nm, with λmax = 250, 205, and

The dialkylmetal azides [(CH3)2AlN3]3, [(C2H5)2GaN3]3, [(C2H5)2,InN3]2 and [(C2H5)2TI]+N−3 were prepared from the corresponding metal trialkyls and chlorine azide. Their properties are given and their structures were determined from their vibrational spectra (IR and Raman). The trimeric azides of Al and Ga form planar six-membered metal-nitrogen rings (symmetry D3h), the dimeric azide of indium probably forms a planar four-membered In2N2-ring and the structure of diethylthallium azide is ionic.

The microwave spectra of four isotopic species of chlorine azide, ClN3, have been observed in the frequency range 26–48 GHz. From the measured values of the rotational constants, the molecule has been deduced to be planar with the following internuclear parameters: r(Cl–N(1)) = 1.745 ± 0.005 A, r(N(1)–N(2)) = 1.252 ± 0.010 A, r(N(2)–N(3)) = 1.133 ± 0.010 A, ∠ClN(1)N(2) = 108°40′ ± 30′, ∠N(1)N(2)N(3) = 171°56′ ± 30′, with Cl and N(3) trans. Values for the chlorine quadrupole coupling constants were obtained for all isotopic species, and for the most abundant, 35Cl14N3, were transformed into the principal field gradient axis system. The values obtained are consistent with the deduced structure.