Spin–Orbit Relaxation of Hg(6³P₁) by Various Gases

Abstract

The spin-orbit relaxation of Hg(6,P1) to yield Hg(6,P0) was investigated in the presence of various gases. The quantum yields of Hg(6,P0) formation (defined as relaxation to Hg(63Po)/total relaxation) in the presence ofCO, CO,, NH,, ND,, H,O, D,O, C2H6, C(CH,),, C3H,, 2,2-C3H6D2, C3D,, n-C4H,, and i-C4Hlo were: 0.88 + 0.07, <0.01, 1.05 + 0.05, 1.00 k0.08, 0.76 + 0.18, 1.06+ 0.26, 0.64 k0.16, 0.56 40.10, 0.58 +0.02, 0.14+0.01, 0.51 k0.07, 0.47+0.10, 0.11 k0.01, and 0.05+0.01, respectively. The extent of the spin-rbit relaxation process appears to be related in an inverse manner to the availability and accessibility of channels leading to the formation of Hg(6'S0), rather than to the fulfillment of electronic-vibrational resonance conditions. This in turn suggests the existence of Hg(63Pl)--quencher intermediates having lifetimes long enough to permit several vibrations.La relaxation spin-rbitale de Hg(6,P1) pour donner Hg(6,P0) a tte etudike en presence de nombreux gaz. Les rendements quantiques de la formation de H~(~, P , ) (definis par relaxation de H~(~, P , ) sur relaxation totale) en presence de CO, CO,, NH,, ND,, H,O, D,O, C,H6, c-C,H6, C(CH,),, C3H8, 2,2-C3H6D,, C3D8, n-C4Hlo et i-C4Hlo sont: 0.88 + 0.07, 10.01, 1.05 + 0.05, 1.00 + 0.08, 0.76 + 0.18, 1.06 + 0.26, 0.64 + 0.16, 0.56+0.10, 0.58+0.02, 0.14+0.01, 0.51 k0.07, 0.47+0.10, 0.11 k0.01 et 0.05+0.01. Le domaine du procCd6 de relaxation spin orbitale apparait comme ttant en sens inverse de la disponibilite et de I'accessibilitC des canaux menant a la formation de Hg(6'S0) plutBt que du remplissage des conditions de resonance electronique-vibrationnelle. Ceci suggkre I'existence d'intermtdiaires de pitgeage Hg(6,P,) qui ont des temps de vie assez longs pour permettre plusieurs vibrations.Canadian Journal of Chemistry, 50, 176 (1972) In a recent communication from this laboratory (1) we have presented preliminary data on the spin-orbit relaxation of Hg(63Pl) atoms to yield Hg(63Po) in the presence of various gases. Because of the importance of these measurements in the elucidation of the energy transfer process in mercury photosensitization (2-9) and the controversial nature of the problem (10-14), we have investigated the spin-orbit relaxation process in greater detail and extended our measurements to more molecules. Particular attention was focused on molecules such as CO, CO,, H,O, D,O, NH, and ND,, that have been previously considered ( 2 4 , 10, 15) from the point of view of the resonance theory of spin-orbit relaxation,The relative increase of the total ~g ( 6~~, ) quenchingcross section with the relative decrease of the energy discrepancy, AE, of the electronic and the vibrational transition, were cited as basis for the resonance theory. However, there were only few direct measurements such as rate constants for the occurrence of reaction 1. The result of Scheer and Fine (10) for CO has recently been questioned (14, 126).Also, of particular interest were the alkanes which have been thoroughly studied in the past and were shown to exhibit a num...

Reactions of hydrogen atoms with hexafluoroacetone

“…It was argued (1 2) that any excited spec~es produced in the latter quenchlng processes would be quicltly deactivated at these near-atmospheric pressures to return to the ground state without decornpos~tion. This assumption IS nobv harder to justlfy as more recent work has shomn the quenchlng of Hg(3P,) to Hg(3P,) and subsequent quench~ng of HE(~P,) to be more ~mportant than was previously suspected (9) Hobever. if the mechanisms are modified to ~nclude the effects of mercury lnetastables they become Intractable…”

“…niolpl s -' and that for H + C2H, 1s known to be 7 x 108 e mol-' s-' (13). Therefore under the above condit~ons, the reaction of H + H F A I S almost negllg~ble and the assuniptlon that reaction [9] been made that all of the atomic hydrogen reacts with ethylene to give ethyl radicals. The plot of this equation is shown also in Fig.…”

“…Since 111 t h~s bvork wle have ollly been concerned ~~t h the ratios of quench~ng constants, ~t 1s doubtful that the absolute values are of much Importance The latter coinment lndy also be appl~ed to the crltlc~sm of the N,O techn~que by Vlkls ct 01. (9,11 ) u ho expla~ned the divergence between the chemical and physlcal measurements of k, by showlng that the effect of Hg('PO) had been neglected in the former.…”

“…If it is assumed that HFA behaves l~k e an olefin, and that the ~n~t i a l l y formed adduct between H and HFA subsequently decomposes with unit efficiency, then reactions [5], [7], and [8], respectively, would be replaced by : [9] H + HFA -. HCF,CO f CF3…”

“…Equatlon [12] is plotted In Fig. 3 The piedlcted l~near dependence 1s found but it IS also noted that the slope depends on the absolute value of [C2H,] Thls latter result is not compat~ble with the niechanlsrn An ~niportallt process whlch has been Ignored is undoubtedly the rad~cal exchange reactlon b e t~e e n ethyl radlcals and HFA: slmllar reactions ale knov~n (2, 3) [13] CzHs + (CF3)2C0 + C2H5CF3C0 + CF3 If this reaction is included in the kinetic scheme, and [9] is omitted, and it is assuilied again that radical interaction rates are equal, i.e. 2/< = 2(k,…”