正丙醇和异丙醇的紫外光解动力学

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——————————————————————————————————————————————————————————————1003-7713/2002/03-233-4
兴Pro ect su pp orted b y the U.S.NationaI Science Foundation （CHE-0111635）and the AIfred P.SIoan Foundation.Dedication to Professor Lou Nan g uan on the occation of his 80’s birthda y .兴兴Corres p ondin g author ；fax ：909-787-4713；E-maiI ： in g son g .zhan g @ ；aIso at Air PoIIution Research Center ，Universit y of CaIifornia ，Riverside ，CA 92521.Received date ：2002-05-01.
Ultraviolet Photodissociation D y namics of
1-Pro p anol and 2-Pro p anol b y Hi g h-!
R y dber g -atom Time-of-fli g ht
（HRTOF ）Techni g ue 兴Zhou Weidon g ，Zhan g Jin g son g 兴
兴（De p artment O f Chemistr y ，Uniuersit y O f Cali f Ornia ，Riuerside ，CA 92521）
abstract 193.3nm p hotodissociation d y namics of et-cooIed 1-p ro p anoI and 2-p ro p anoI has been examined b y usin g hi g h-n R y dber g -atom time-of-fIi g ht
（HRTOF ）techni g ue.Isoto p e IabeIin g stud y indicates that O -H bond fission is the p rimar y H-atom p roduction channeI.Center-of-mass
（CM ）p roduct transIationaI ener gy reIease of this channeI is Iar g e ，with 〈f T 〉=0.76for H +1-p ro p ox y and 0.78for H +2-p ro p ox y .Maximum CM transIationaI ener gy reIease y ieIds an u pp er Iimit of the O -H bond dissociation ener gy ：（43212）kJ /moI in 1-p ro p anoI and （43312）kJ /moI in 2-p ro p anoI.H-atom p roduct an g uIar distribution is anisotro p ic
（with !二-0.79for 1-p ro p anoI and -0.77for 2-p ro p anoI ），indi-catin g a short excited-state Iifetime.The 193.3nm H-atom dissociation of both 1-p ro p anoI and 2-p ro p anoI is p rom p t and occurs on a re p uIsive excited-state p otentiaI ener gy surface.Ke y words
Photodissociation d y namics ，1-p ro p anoI ，2-p ro p anoI
CLC number ：O 64
Document code ：A
1Introduction
UItravioIet
（UV ）p hotochemistr y of smaII satu-rated aIcohoIs via the first UV absor p tion bands
（S 1卜S 0）has been studied before ［1-10］
.These UV absor p -
tion bands are centered at 185nm ；the y are broad ，featureIess ，and nearI y identicaI.The transition is due to p romotion of an eIectron from the non-bondin g 2p !orbitaI on the ox yg en atom to an excited orbitaI which
has been described as either an antibondin g "兴（O -H ）orbitaI ，a 3s R y dber g orbitaI or a combination of
both （n o 一"
兴/3s ）［11，12］.It is weII known that CH 3OH 一CH 3O +H is the dominant fra g mentation channeI in the UV p hotodis-sociation of methanoI via its first absor p tion band be-tween 165200nm ［1-3，5，6］
.TransIationaI ener gy re-
Iease and an g uIar distribution of this channeI have been measured b y Do pp Ier broadened fIuorescence Iine
sha p e of the nascent H-atoms ［5］
and the HRTOF
techni g ue
［6］
，indicatin g that the first eIectronic excit-ed state of CH 3OH （via n o 一"兴/3s ）is re p
uIsive in the O -H coordinate and dissociates ra p idI y .The
concIusion is consistent with the theoreticaI studies of
methanoI p hotochemistr y ［8-10］
.
SimiIarI y ，the O -H bond cIeava g e is the main
dissociation channeI in the UV p hotoI y sis of ethanoI
via its first absor p tion band ［1-3，6，7］
.A Iar g e fraction of
the
avaiIabIe ener gy is channeIed into transIation of
the H +ethox y fra g ments ，with 〈E T 〉
=0.84E avaiI at 193.3nm p hotoI y sis ［7］
.A p er p endicuIar eIectronic transition with an anisotro p ic p arameter （!=-0.9）has been observed at 193.3nm ，simiIar to that of
methanoI.The simiIar behaviors observed in the UV
p hotoi y sis of smaii aicohois are consistent with their simiiar and iocaiized eiectronic excitations，in which a ione-p air p!eiectron on the ox yg en atom is p romoted to the antibondin g"!（O-H）orbitai or3s R y dber g orbitai that under g oes ra p id dissociation.
Com p ared to methanoi and ethanoi，p hotochem-istr y of p ro p anoi is iittie studied［2-4］.H-atom eiimi-nation has been re p orted to be im p ortant in the p ho-toi y sis of1-and2-p ro p anoi，which com p etes with other dissociation p athwa y s invoivin g C-C and C-O bond fission［2-4］.However，the fra g mentation mech-anism is stiii unciear.In this work，the hi g h-n R y d-ber g-atom time-of-fii g ht（HRTOF）techni g ue is a p-p iied to stud y the H-atom eiimination channei in the UV p hotoi y sis of1-and2-p ro p anoi.Product center-of-mass（CM）transiationai ener gy and an g uiar distri-butions are obtained，reveaiin g the detaiied p hotodis-sociation d y namics of the p ro p anois.
2Ex p eriment
The HRTOF setu p has been described p revious-i y7，13-16.A p uised moiecuiar beam was p roduced b y ex p andin g a mixture of2%5%p ro p anoi in He（at a totai p ressure of120kPa）into the source chamber，and was coiiimated b y a1mm diameter skimmer at 2.5cm downstream.Both1-and2-p ro p anoi sam p ies were commerciai p roducts（Fisher，99.7%p urit y）and were used without further p urification.At5cm downstream the skimmer，a193.3nm p hotoi y sis ra-diation（t yp icaii y3mJ from an ArF excimer iaser，fo-cused with a70cm f.l.iens）crossed with the moiecuiar beam.For an g uiar distribution measure-ments，the193.3nm radiation was p oiarized with a ten-p iate stack of UV fused siiica siides p iaced at the Brewster's an g ie，with a de g ree of p oiarization of-90%.The H-atom p hoto p roducts resuitin g from the 193.3nm p hotoi y sis of p ro p anois were first excited to the22P state b y the L y man-#radiation at121.6nm，and were further excited to a hi g h-n R y dber g state （n4090）b y a UV radiation at366nm.The L y-man-#radiation was g enerated b y tri p iin g the364.7 nm out p ut of a d y e iaser in a Kr ceii.The hi g h-n R y-dber g H-atom fra g ments are radiativei y metastabie and drifted with their nascent veiocities toward a mi-cros p here p iate detector，and were detected after be-in g fieid-ionized in front of the detector.The nominai fii g ht ien g th was37.1cm.The TOF s p ectra were recorded and avera g ed b y usin g a muitichannei scaier. The H-atom TOF s p ectra p resented here re p resent the resuits of50thousands iaser shots.
3Results and discussion
The H-atom TOF s p ectra from p hotodissociation of1-and2-p ro p anoi at193.3nm are shown in Fi g.1 a and b，res p ectivei y.The arrivai times in both s p ec-tra are in the ran g e of2030$s.The corres p ondin g CM p roduct transiationai ener gy distributions P（E T）' s，which are converted from the H-atom TOF s p ec-tra［16］，are shown in Fi g.2a and b.Preiiminar y re-suits from isoto p e iabeiin g studies indicate that O-
H
Time of fii g ht/$s
Fi g.1H-atom TOF s p ectra from p hotodissociation of
p ro p anois at193.3nm（iaser p ower was3mJ/p uise
）
CM transiationai ener gy/（kJ/moi）
Fi g.2CM p roduct transiationai ener gy distributions P（E T）'s
derived from the TOF s p ectra in Fi g.1
432
bond fission is the p rimar y H-atom p roduction channeI in p ro p anoIs.The p hotoI y sis p ower de p endence of the H-atom TOF s p ectra and the maximum transIationaI
ener gy reIease in the P （E T ）'s are consistent with one-p hone p hotodissociation p rocesses in both 1-and
2-p ro p anoI in this ex p eriment.
The P
（E T ）'s of both CH 3CH （OH ）CH 3and C 2H 5CH 2OH p hotodissociation are g uite Iar g e.The fraction of the totaI avaiIabIe ener gy into fra g ments'transIation is f T =0.76for 1-p ro p anoI and 0.78for 2-p ro p anoI.These resuIts are simiIar to that of 193.3
nm p hotoI y sis of methanoI ［6］
with f T =0.82and ethanoI ［7］with f T =0.8.Such a Iar g e p roduct trans-IationaI ener gy reIease su gg ests a ra p id dissociation
takin g p Iace on a re p uIsive p otentiaI ener gy surface （PES ）before internaI conversion.In addition ，both
p ro p anoIs have nearI y identicaI P
（E T ）'s in the H-atom eIimination p rocesses ，indicatin g ver y simiIar
dissociation mechanisms.
From the measured maximum transIationaI ener-
gy reIease and the p rinci p Ie of ener gy conservation ，an u pp er Iimit of the bond dissociation ener gy ，D 0（C 2H 5CH 2O-H ）and D 0（（CH 3）2CHO-H ）
，can be estimated ［16］
.With a maximum transIationaI ener gy reIease 187kJ /
moI for 1-p ro p anoI ，a vaIue D 0（C 2H 5CH 2O-H ）!（43212）kJ /moI is derived.The uncertaint y in de-terminin g the bond ener gy is 2kJ /moI ，incIudin g the p hotoI y sis Iaser Iinewidth and the uncertaint y in
identif y in g the maximum ener gy reIease.This resuIt of D 0（C 2H 5CH 2O-H ）is in g ood a g reement with the
430kJ /moI vaIue b y Ross et al.
［4］
.SimiIarI y ，an O -H bond ener gy in 2-p ro p anoI is derived to be （433
12）
kJ /moI.The H-atom p roduct an g uIar distributions in the
1-and 2-p ro p oanoI dissociation have been investi g ated b y usin g IinearI y p oIarized Iaser radiation.Fi g .3shows the H-atom TOF s p ectra from p hotodissociation of 1-p ro p anoI b y p oIarized 193.3nm Iaser with its p o-Iarization direction p araIIeI or p er p endicuIar to the TOF axis.LinearI y p oIarized Ii g ht p referentiaII y ex-cites those sam p Ie moIecuIes with their eIectronic tran-sition di p oIe moment p araIIeI to the eIectric vector !of the p oIarized Iaser radiation.The p hotofra g ment
an g uIar distribution is g iven b y
［17］
I （!）=（1/4）"［1+#P 2（cos
!）］where #is the anisotro py p arameter （-1!!
!2），!is the an g Ie between the eIectric vector of the p oIarized Iaser radiation !and the recoiIin g veIocit y vector
of the H-atom p roduct （the direction of detection ），and P 2（cos !）is the second Le g endre p oI y nomiaI.
From the measured H-atom TOF s p ectra with the p o-Iarized p hotoI y sis radiation ，a si g nificant anisotro py in the an g uIar distribution is observed.After the correc-tion for im p erfect p oIarization of the p hotoI y sis Ii g ht ，a s p atiaI anisotro py p arameter #"-0.79is obtained for 1-p ro p anoI and -0.77for 2-p ro p anoI.This ne g a-tive #vaIue indicates that the transition di p oIe mo-ment is p er p endicuIar to the O -H bond from where the H-atom recoiIs ，and that the p ro p anoI moIecuIe dissociates in a time scaIe that is shorter than its rota-tionaI p eriod.Thus it is concIuded that the dissocia-tion of O -H bond in the p ro p anoIs at 193.3nm is a p rom p t p rocess ，which IikeI y occurs on a re p uIsive ex-
cited-state PES.The #vaIues for the p ro p anoIs are simiIar to the re p orted vaIues for methanoI （#=-0.
60or -0.70）［6］and for ethanoI （#=-0.90）［7］.
Time of fIi g ht /"s
Fi g .3
H-atom TOF s p ectra of 193.3nm p hotodissociation of 1-p ro p anoI ，with the p oIarization !vector of the p hotoI y sis radiation p er p endicuIar and p araIIeI to the TOF axis The si g naIs have been normaIized to the same Iaser p ower and Iaser shots.
In the UV p hotoI y sis of methanoI and ethanoI ，the O -H bond fission has been shown to be the main source of H-atom p roducts and aIso the ma or dissocia-tion channeI ［6，7］
.In the earI y p hotochemistr y stud y of 2-p ro p anoI ，the H-atom p roduct channeI has aIso
5
32
been identified as the p redominant p athwa y［3］.In ad-
dition，the d y namic information of the p hotodisso-ciation of both p ro p anoIs（such as P（E T）'s and an g u-Iar distributions）is essentiaII y identicaI，and is aIso ver y simiIar to that of methanoI and ethanoI.This is consistent with the common nature of the first eIec-tronic excited states of these smaII saturated aIcohoIs. The first absor p tion bands of methanoI，ethanoI and p ro p anoIs have identicaI sha p e and Iocation，and the corres p ondin g eIectronic excitation via the I o!!"/3s transition is Iar g eI y Io-caIized on the H-0-C moiet y and is essentiaII y the same for these smaII aIcohoIs.With the IocaIized exci-tation in H-0-C and the re p uIsive nature of the first eIectronic excited state（aIon g the0-H coordi-nate），the UV p hotodissociation of1-and2-p ro p anoI is simiIar to that of methanoI and ethanoI，and the H-atom dissociation channeI in p ro p anoIs is p rom p t and occurs on a re p uIsive excited-state PES.
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正丙醇和异丙醇的紫外光解动力学"
周卫东，张劲松""
（美国加州大学河滨分校化学系，加州河滨市92521）
摘要：利用高里德堡态氢原子飞行时间（HRT0F）探测技术，研究了正丙醇和异丙醇的紫外光解动力学过程.在193.3nm光辐射下，0-H键快速断裂过程构成主要的氢原子生成通道.伴随0-H键的碎裂，相当大的一部分能量转换成氢原子及其相应碎片的平动能（正丙醇〈f v〉=0.76；异丙醇〈f v〉=0.78）.氢原子碎片具有各向异性的角度分布；其角分布异向因子!分别为-0.79（正丙醇）和-0.77（异丙醇）.研究结果表明，吸收1个193.3nm光子后，丙醇分子跃迁到一个寿命很短的电子激发态；沿着0-H反应坐标，该激发态势能面是排斥的，因而0-H键快速断裂.此外，还得到了丙醇的0-H键离解能：（43212）kJ/moI（正丙醇）和（43312）kJ/moI（异丙醇）.
关键词：光解动力学；正丙醇；异丙醇
中图分类号：064文献标识码：A
"美国自然科学基金（CHE-0111635）和AIfred P.SIoan基金资助项目.祝贺楼南泉院士80华诞.
""通讯联系人，E-maiI：in g son g.zhan g@
632
正丙醇和异丙醇的紫外光解动力学
作者：周卫东， 张劲松
作者单位：美国加州大学河滨分校化学系,加州河滨市,92521
刊名：
化学物理学报
英文刊名：CHINESE JOURNAL OF CHEMICAL PHYSICS
年，卷(期)：2002,15(3)
被引用次数：3次
1.von Sonntag C;Schuchman H P查看详情[外文期刊] 1977
2.Von Sonntag C;McGlynn S P in Photophysics and Photochemistry in the Vacuum Ultraviolet 1985
3.Calvert J G;Pitts J N Jr Photochemistry 1966
4.Zare R N查看详情 1972
5.Zhang J;Dulligan M;Wittig C查看详情 1995
6.Ashfold M N R;Lambert I R;Mordaunt D H;Morley G P,Western C M.查看详情 1992
7.Schnieder L;Meier W;Welge K H查看详情 1990
8.Zhang J;Xu K;Amaral G查看详情 1999
9.Robin M B;Kuebler N A查看详情 1972(01)
10.Robin M B Higher Excited States of Polyatomic Molecules 1985
11.Marston C C;Weide K;Schinke R查看详情[外文期刊] 1993
12.Kassab E;Gleghorn J T;Evleth E M查看详情 1983
13.Buenker R J;Olbrich G;Schuchmann H P;Schurmann B L,von Sonntag C查看详情[外文期刊] 1984
14.Xu K;Amaral G;Zhang J查看详情 1999
15.Wen Y;Segall J;Dulligan M;Wittig C.查看详情[外文期刊] 1994
16.Satyapal S;Park J;Bersohn R查看详情[外文期刊] 1989
17.Ross P L;van Bramer S E;Johnston M V查看详情[外文期刊] 1996
1.陈砺.周传华.严宗诚.王红林正丙醇溶液直流辉光放电等离子体电解产物分析[期刊论文]-科技导报 2010(5)
2.朱拓.陈国庆.虞锐鹏.刘莹.倪晓武醇类溶液的紫外吸收和荧光光谱研究[期刊论文]-光谱学与光谱分析 2006(2)
3.朱拓醇类物质光谱学和光子密度波扩散理论研究[学位论文]博士 2005
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