Hydrogen vibrationally excited, reaction

The primary and secondary products of photolysis of common diazirines are collected in Table 4. According to the table secondary reactions include not only isomerization of alkenes and hydrogen elimination to alkynes, but also a retro-Diels-Alder reaction of vibrationally excited cyclohexene, as well as obvious radical reactions in the case of excited propene. 

In order to form the biradical (133), the cyclopropane molecule becomes vibrationally excited by collision with another molecule the C—C bond may then break provided the extra energy is not lost too rapidly by further collision. There is driving force here for a 1,2-shift of hydrogen—unlike in mono-radicals (p. 335)—because of the opportunity of electron-pairing to form a n bond (with evolution of energy) in (134). There is evidence that this H-migration is commonly the rate-limiting step of the reaction. 

Chemiluminescence is observed from several different emitting species, depending on the analyte and reaction conditions. Vibrational overtone bands of HF in the wavelength region of =500-900 nm are observed under nearly all conditions and are often the dominant spectral feature, the (3,0), (4,0) (5,1), and (6,2) bands being the most intense, while for some reaction conditions emissions from levels up to v = 8 are observed [63], It is likely that hydrogen atoms are produced in the reaction and form vibrationally excited HF in the reaction reported by Mann et al. [62] ... 

An alternative LIS scheme is one in which a vibrationally excited molecule reacts preferentially with another species. An example is the hydrogen halide/olefin addition reaction, DX + RiR2C = CH2 RiR2CXCH2D. The scheme involves sequential absorption of several quanta from a C02 laser near 5 p,m to selectively excite DX to a vibrational quantum number of 3 or more. Successful implementation would be expensive because of the highly corrosive nature of halogen acids. 

It emerges from this finding that the entire energy generated by these reactions does not go into vibrational excitation of the W-C bonds when the hydrogen sites are replaced by steps lb and 2a from Table 1. Over half of the species survive in a 36 step free radical reaction. Each of these steps generates, of the order of, 100 kcal mol-1 of energy. 

Cashion and Polanyi83 and Clement and Ramsay96 examined the red emission from about 6000 to 10,000 A resulting from the chemiluminescent reaction of hydrogen atoms with nitric oxide. The former authors observed emission from both vibrationally excited (2.9-3.6 p.)... 

Under 300 K ambient conditions, reactions of photolytically produced fast hydrogen atoms with C02 are known to yield OH + CO products via vibrationally excited HOCOt intermediates. Since the initial report by Oldershaw and Porter (1969), many groups have studied reaction (1) by using fast hydrogen atoms and... 

Figure 3-9. Sub-Doppler resolution OH LIF spectra indicate a modest amount of c.m. translational energy for all of the OH levels monitored in the reaction H + N20 -> OH + N2 see Bohmer et al. (1992) for details. A Franck-Condon projection of the 1,3-hydrogen shift transition state N-N separation of 1.23 A (solid line, lower part) predicts a high degree of N2 vibrational excitation (upper part) and yields good agreement with the data (shaded circles, lower part).

Figure 3-14. Schematic drawing of the photoinitiated reaction of Br with I2. Hydrogen removal is rapid, relative to the characteristic time scales of the motions of the heavier nuclei. Photoexcitation at 220 nm yields primarily Br(2P3/2), though some Br(2P1/2) is also produced. As shown on the right, reaction transpires via the vibrationally excited trihalogen intermediate.

Arrivo SM, Heilweil EJ. Conservation of vibrational excitation during hydrogen bonding reactions. J Phys Chem 1996 100 11975-11983. 

---