Gas phase far ultraviolet photolysis and radiolysis of vinyl chloride

Abstract

Quantum yi e lds of the major produ cts formed in the far ultravi ole t photolys is of CH,C DCI (C2 H2 , C, HD , C,HoD, C, H2 D" and 1,3·C, H,D,) have bee n de te rmin e d at 147 nm (8.4 e V), 123.6 nm (10.0 eV), a nd 104.8-106.7 nm 01.6-11.8 e V). The quantum yield of th e s tab le vinyl rad ica ls whi c h can be un· ambiguous ly asc ribed to the primary process (C H2CDCI + hll~ CH,C D+ CI) is 0.3 a nd 0.05 at 147 and 123.6 nm, res pe c tive ly. The sharp d ec rease in the yie ld of vinyl radicals with the in c re ase in e ne rgy of the in cid e nt photon beam is in part attribute d to the deco mposition of inte rnally e xcited vinyl radica ls to give acet yle ne as a produ c t. At 147 nm , th e co mbin ed yield of acet yle ne plu s vinyl rad icals is 0.95 ± 0.05. At the s horte r wa ve length s, approximate ly one acet yle ne molecul e is form ed per e lectronically excite d vinyl c hloride mol ec ule. It is conclude d that th e dissociative process: C2 HaCI* ~ C,H, + H + CI, occ urrin g via a C, Ha or C,H, CI inte rm e diate ade qu ate ly acco unts for the reo active ne utral s pecies form ed at higher photon e ne rgies. Isotopi c la belin g e xpe rim e nts s how that the hyd roge n atoms are d etac hed from both pos iti ons of th e pare nt molecule. Ethylene whic h is a produ ct over the e ntire wavel ength range is in part form e d via the reaction : H* + C,HaC I ~ C2H .. + CI, whe re H* re presents a translationa Uy e xcited hydrogen atom. The C2H2DC I+ ion s formed at 104.8 -106.7 nm with a quantum yie ld of 0.47 do not contribute to th e form ation of acetyle ne or vinyl radi c al s. In the gas phase radiolysis of vinyl c hlorid e, acetyl e ne (G -1. 5) is ma inly form e d in th e di ssocia tion of ne utra l e lectronica ll y excited vinyl c hlorid e molec ules. From this value, we may es tim ate th at the ratio of neutral excited molec ul es formation to ionization in th e rad iolys is of vinyl c hl orid e is 0.39. Vinyl ions, whi c h a re also prod uced (G -0.28-0.35) react ma inl y by addition to vi n yl c hlorid e.

ChemInform Abstract: PRIMARY STEPS IN THE PHOTOLYSIS OF CIS‐1,2‐DICHLOROETHYLENE

“…(1 1) may be omitted provided it is accepted that a large fraction of the excited CHClCH radicals carry so much energy that they cannot be deactivated and will decompose before colliding with neighboring cis molecules. This parallels the results obtained in the photolysis of C2H3C1 at low wavelengths where the authors stated that the reaction Calculations, as given earlier, yielded 3.8 X CzH3Cl + hv + CzHz + H + C1 may or may not occur via an excited radical [8].…”

“…Thus we obtain k11/k7 = 5.0 and k 9 / k s = 1.3 X lo-'* (mole/cm3)-'. These data indicate that at zero pressure about 17% of the acetylene produced by the "two star" excited state originates from reaction (8) and about 83% of,,, reaction (1 1).…”

“…Later work by Ausloos and coworkers [8] indicates that at shorter wave-C2H3Cl** -+ C2Hz + H + C1 which may proceed via an excited C2H3 or CZHzC1 radical.…”

“…(lb) (7) (8) CzHzClO-+ CzHz + C1 Figure 6 and shows a linear relationship between R c~H~( * * ) / R c~H~c I I ( * * ) and l/(CzHzClZ). There is, however, a distinct intercept indicating that the present mechanism does not account for all the CzHz produced by the "two star" excited state.…”

I. Three-center versus four-center HCl-elimination in photolysis of vinyl chloride at 193 nm: Bimodal rotational distribution of HCl (v⩽7) detected with time-resolved Fourier-transform spectroscopy

“…Ausloos et al 9 observed a nearly equal yield from three-center and fourcenter elimination in the spectral region 200-220 nm, with the former decreasing in importance at shorter wavelengths. Berry 2 reported a quantum yield of HCl from CH 2 CDCl 92% of that from CH 2 CHCl for у155 nm, indicating that fourcenter HCl-elimination is the major channel.…”