Photoionization of propylene, cyclopropane, and ethylene. The effect of internal energy on the bimolecular reactions of C2H+4 and C3H+6

Abstract

Th e ion·mo lec u le c he mi s t ry occ urrin g in photo ion ized eth yle ne . prop yle ne a nd cyc lop rop an e ha s bee n in ves tiga ted in th e N BS hi g h press ure ma ss s pect rome te r. Empha s is has bee n pl ace d on d ete rmin ing th e ove ra ll e ffe c t of int e rn a l e xc it ati o n o n th e abso lut e ra te c oe ffi c ie nt s for th e va ri o us re ac ti o ns. T hi s was acco mpli s he d by c o mpari ng th e be h av ior fo und wh e n ioni za ti on was in du ced by photon abso rpti o n at th e ion iza ti o n thres hold with th a t fo un d at hi ghe r photo n e ne rgies. T he va lu es fo r th e a bso lute rat e coe ffic ie nt s fo r th e formation of e xc it ed co mpo und io ns at variou s photo n e ne rgies we re a s foll o ws (unit s of 10-'0 c m"/ mol ec ul e ' s); C, H.i . 9.6 (10.6 e V phot o ns) ; 8.5 (l 1. 7 eV phot o ns); G, H, ; .8.4 (10. 0 e V photo ns); 6.8 (11.7 e V photon s); G,D,! . 7.8 (10.0 e V p ho ton s). 6.1 (1 1. 7 e V pho ton s) ; c-C Hi, a nd c-G. D, ; . 2.2 (10.0 e V photon s); 2.2 (1 1. 7 e V photo ns). Th e di s trib ut io ns of prod uc t io ns o btain ed f ro m th e unim o lec u lar decompos iti o n of th e co m pound io n in eac h s ys te m hav e a lso bee n dete rmin ed a t vario us photon e nergies . a nd co ns id e rab le va ri a ti o n has bee n o bse rve d. In ge ne ra l. th e va ri a ti o ns a re s imil ar to those fo un d e lse wh e re whe n th e kineti c e ne rg y of th e re ac ta nt ion is in c reased. Th e bimo lec ul a r rea c ti o ns of th e C" D;', co mpound io n ob tai ne d fro m C, D,; hav e bee n inv es ti ga ted a t hi ghe r press ures. and se para te ex pe rim e nt s in vo lvin g isotop ica ll y la be le d e thy lenes have prov ided ne w informa ti o n co nce rnin g th e nature of th e co mpound ion in th at s ys te m . Res ul t s ob t ained from o th e r laborator ies a re di sc usse d in s ome de ta il. a nd in mos t ca ses th e diffe re nces found fo r th e s ame s yste m a re ex pli c ab le in te rm s of th e e ne rgy co nt e nt (int e rn a l a nd/o r kin e ti c) of th e re ac ta nt ion . .Key wo rds : Co lli s iona l sta bi li za ti on; hyd rocarbo ns; ion -mo lecu le reac ti o ns : photoioni za tion; ra te c on stant s; stru c tures of iOll s. . IntroductionAlth ough a great deal of inform a ti on has been acc umul a ted co ncernin g the effec t of ion kin e ti c e nergy on the rates and mec hani s ms of ion-molecule r eac tions [1],' th e effects of inte rnal e nergy re main relatively un ex plored. However, several recent in vestigations [2] of proton tran sfer reactions occurring in inorga ni c syste ms usin g hi gh resolution photoionization mass spectrometry have demons trated that th e cross sec tions for ce rtain processes may be extremely sens iti ve to c ha nges in th e vibrational e ne rgy co nte nt of th e reactant ion. Thi s be havior was quantitatively investigated in a recent s tudy from thi s laboratory [3] , whi c h involved a de te rmination of the absolute rate coeffi cient for th e reaction NHt + NH:j ~ NH! + NH2 as a fun ction o...

Photoionization of C4H+8 isomers. Unimolecular and biomolecular reactions of C4H+8 ions

“…The analogous reaction scheme has been found in propylene, although the rate of dimer formation and its subsequent reaction was approxi· mately a factor of four slower than found in isobutene. These results have recently been discussed [13]. The formation of stable dimeric ions and their sub· sequent reactions has not been considered previously when interpreting the radiation·induced polymeriza· tion of isobutene, but the present data indicate that this mechanism will contribute significantly to the chemical e nd-products.…”

“…Also included are the ! :iH J valu es for th e pare nt ion s. Th e major di ssociative processes found we re: (11) ( 12) Th e minor di ssociation: (13) was also observed for every isomer , and th e fragm ent CzH: ion was observed from c-C 4 Hs.…”

Insights into the C4H8+· potential energy surface: Fourier transform ion cyclotron resonance studies of ion-molecule reactions of D-labeled partners

“…14, 15 It shows an H-D exchange prior to dissociation, assuming a k H /k D D 2 isotope effect for the final C-H or C-D cleavage.…”

“…15 They were reinvestigated here using FT-ICR with relaxed ions and with ions selectively produced in an external ion source. This method has the advantage of determining unambiguously the studied reaction as the reactant ions were first generated in the external ion source and were then transferred into the cell containing the neutral reactant, avoiding therefore any crossreaction involving other ionic or neutral species.…”

Molecular Beam Photoionization and Photoelectron-Photoion Coincidence Studies of High Temperature Molecules, Transient Species, and Clusters

“…In the region of 1000-1270 A, the relative abundances are in the order I(C 4 H 8 + ) > I(C 5 H 9+ ) > I(C 4 H 7 + ), and are in qualitative agreement with those found for the C 3 H 6 + + C^ reaction induced with 10.0 and 11.7 eV photons in a single chamber photoionization mass spectrometric study. 166 The relative abundance for C 4 Fig. 30 than in Fig.…”