This paper reports CO(v,J) distributions from photolysis on the 2141, 45, 2161, 2143, and 2341 bands of H2CO and the 2243 band of D2CO. A significant fraction of the CO(v=0) photofragment is found in low rotational states (JCO<15) for excitation above the threshold of the H+HCO dissociation channel. Photolysis on the 2141 band, which lies below this radical threshold, shows no measurable population in low-JCO states. The fraction of the total population in low-JCO states increases with increasing photolysis energy. In contrast, the CO(v=1, J) distributions do not broaden significantly with increasing excitation energy. Similar results are found for D2CO. Two alternative models addressing the dynamics of this dissociation are proposed. First, anharmonic motion at the transition state may lead the molecule to dissociate from configurations with smaller impact parameters and thus produce a broadened rotational distribution. More likely, a second fragmentation path, related to the exit channel of the H+HCO→H2+CO abstraction reaction and accessed through the radical channel, may open.

Phase transitions in the α‐, β‐, γ‐, and ϵ‐polymorphs of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Described are the results of high temperature equilibrium solvation studies coupled with Fourier transform infrared spectroscopy (FTIR) for the identification of polymorphic conversion. These results are augmented by data in Part II from differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and optical hot stage microscopy(6). The thermodynamic stability order of ϵ > γ > α‐hydrate > β is shown, with the epsilon polymorph the most thermodynamically stable phase of HNTW at room temperature. The existence of multiple α‐hydrate phases is shown to complicate the determination of the equilibrium P‐T phase diagram of HNIW.

Solid‐solid phase transitions in the α‐, β‐, γ‐, and ϵ‐polymorphs of 2,4,6,8,10,12‐hexanitrohexaazaisowurtzitane (HNIW) have been studied as a function of temperature. Techniques employed include differential scanning calorimetry (DSC), differential thermal analysis/thermogravimetric analysis (DTA/TGA), and hot stage microscope analysis. Fourier transform infrared spectroscopy (FTIR) was used to identify results of polymorphic conversion. Results corroborate those(2) of Part I that the existence of multiple α‐hydrate phases complicates definition of the HNIW P‐T phase diagram. A high temperature endothermic DSC response was determined by FTIR spectroscopy to be the β → γ transition, not a conversion to a new high temperature “delta” phase. The role of water in the shifting this conversion to higher temperature is discussed.

No abstract

Rovibronic state to rovibronic state reaction dynamics: O(3 P)+HCl(v=2,J)→OH(v′,N′)+Cl(2 P) Complete rotational distributions have been obtained for the CO produced following excitation of H 2 CO, HDCO, and D 2 CO near the S 1 origin. The CO was detected by vacuum ultraviolet laser-induced fluorescence. The distributions show a remarkable amount of rotational excitation, peaking at J = 42, 49, and 53 for H 2 CO, HDCO, and D 2 CO, respectively, with widths of 20-25 J units (FWHM). CO(v = 1) from H 2 CO photolysis has nearly the same rotational distribution as CO(v = 0). The population of CO(v = 1) is 14%±5% as large as the population of CO (v = 0), in good agreement with earlier measurements. Increased angular momentum of H CO is only partially transferred to CO, giving slightly wider rotational distributi~ns without changing the peak value. The rotational distributions are highly nonthermal, showing that energy randomization does not occur during the dissociation event. An approximate range of product impact parameters has been determined. The impact parameters are too large to be accounted for by forces along the directions of the C-H bonds. The hydrogen ~ppears to be most strongly repelled by the charge distribution a fraction of an A outside the carbon atom of the CO. The distribution of impact parameters and the internal energy of the hydrogen fragment apparently do not change significantly upon isotopic substitution. The absence of population in CO(J < 20) confirms the identity of CO(J > 25) as the long-lived intermediate in formaldehyde photodissociation.3032