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Re-measurements of partial photoionization cross-sections of CH4, NH3 and H2O at 58.4 nm by He(I) photoelectron spectroscopy
Journal of Electron
Spectroscopy
and Related
Phenomena,
o Elsevler Screntlfx Pubhshmg Company, Amsterdam -
22 (1981) 187-190 Prmted m The Netherlands
Short commumcatlon
RE-MEASUREMENTS OF PARTIAL PHOTOIONIZATION CROSSSECTIONS OF CH,, , NH3 AND H2 0 AT 58 4 nm BY He(I) PHOTOELECTRON SPECTROSCOPY
Y ACHIBA,
T YAMAZAKI
and K KIMURA*
Institute of Applred Electncrty, Hokkaldo Molecular Science, Ukazakz (Japan)
Unluerszty,
Sapporo,
and Instztute
for
(First received 18 March 1980, m final form 9 September 1980)
Klmura et al [I] have previously described a gas-phase photoelectron method that uses a bmary mixture of a standard and a sample m order to obtsun partial photolonlzatlon cross-sections of molecules We have recently Improved this method w&h the ad of a mmlcomputer-based data-processmg system In this commurucatlon, we report some results of our re-measurements of dlfferentlal and partial photolonlzatlon cross-sections of CH4, NH3 and Hz 0 The steps of the process used here are shown m the form of a flowchart in
Fig 1 The dlfferentlal photoloruzatlon cross-section I, = du,/di2 for producmg photoelectrons wlthm the solid angle dS2 at an angle 8 for unpolarized light 1s theoretically related to the part& photoldnlzatlon cross-se&on q
Fig 1 A flowchart mdlcatmg the processes of determmatlon of dlfferentlal and partial photolomzatlon cross-sectlons of molecules * To whom Okazakl444,
correspondence Japan)
should
be addressed (Institute
for Molecular
Science,
188
for producing I,(e)
a specific lonlc state by the expression
= (0,/47r){l-
@,/4)(3
[l]
cos2e - 1))
where p, 1s the asymmetry parameter The He(I) photoelectron spectrometer used here 1s essentially the same as that used previously [ 11, photoelectron spectra being measured at 8 = 90” The mtensltles of the He(I) spectra were corrected for electron collection efficiency on the bans of the mtenslty data for N2, O2 and CO2 reported by Gardner and Samson [3] Relative band mtensltles obtained with respect to the standard were then converted to absolute 1, (90) values on the basis of a reference value of 0 78 Mb for I1=1 (90) of N, derived from eqn (1) using the values 0, =1 = 8 4 Mb and 0, =1 = 0 68 previously reported by Samson et al [4, 51 The features which we have improved for the present photoelectron intensity measurements are the followmg (1) The mole fraction of the sample m each binary mixture introduced mto the lonlzatlon chamber of the spectrometer via a needle valve, was determined by using two vacuum gauges of different types (Baratron and Pram gauges) Previously, it was assumed that the moIe fraction of the sample m the lomzatlon area 1s the same as that m the mltlal gas reservoir In the present study N, was used as a standard for the intensity measurements on both CH4 and NH3, and the mole fractions m the loruzatlon area were carefully determined by analyzing the Baratron and Plranr outputs For HZO, however, we used NH3 as a standard, without any mole fraction correction, since the Plranl gauge used was unstable for H2 0 vapour (For a m&ure of Hz0 and NH3, the mole fraction correction IS probably within 3% ) (2) The number of data sampled durmg photoelectron intensity measurements as well as pressure measurements was much increased by the use of a mmlcomputer (Model YHP 2105A), and the reproduclblhty of the data was repeatedly checked Results obtamed here for 1, (90) and o, of CH4, NH, and H, 0 are summarized m Table 1, and compared with our previous results as well as the electron-impact data on o, reported by Brlon et al [6-81 From Table 1 It can be seen that there are no maJor discrepancies between the three sets of data except for the 2B2 state of H20+ for which much larger values are obtamed m the present study The reason for this 1s uncertain, but one of the reasons may be that the standard devlatlon introduced m the transmlsslon correction above 19 eV IS much larger than that below 19 eV It should be pointed out that care must be taken especially for intensity measurements of low-energy photoelectrons In the present study, only the He(I) 58 4 nm lme was used It IS well known that synchrotron radiation 1s a very useful source for studying a, and @, as a function of photon energy over a wide energy range [ 9, lo]
189
TABLE
1
DIFFERENTIAL AND PARTIAL CH4, NH3 and Hz 0 AT 58 4 nm Molecule
Iomc state
PHOTOIONIZATION
This work
CROSS-SECTIONS
OF
Previous work [ 1 ]
Brlon et al [6-S]
I,(901
4
1,(90)
4
4
(334
T2
3 11
33 9
2 95
32 2
31 1
NH3
Al El
0 63 1 94
65 23 1
0 78 199
81 23 7
57 22 9
Hz0
B1 Al
0 71 0 72 1 14
71 85 14 8
0 59 0 51 0 65
59 60 84
62 58
B2
(Mb)
The present method can, of course, be apphed for synchrotron radratlon The advantage of the present method m usmg a binary gaseous mixture 1s that partial photolonlzatlon cross-sections can be obtamed from measurements of onIy photoelectron mtenslty using a conventional photoelectron spectrometer As already pomted out by Gardner and Samson [3], It 1s desirable to carry out direct photoelectron measurements at the magic angle of 54”44’ rather than at 90”
ACKNOWLEDGEMENT
The authors wish to thank Mr Y Shmdo for his expert advlce on the construction of the data-processmg system
REFERENCES 1
K Klmura, Y Achlba, M Momshlta and T Yamazakr, J Electron Spectrosc Relat , 15 (1979) 269 J C Tully, B S Berry and B J Dalton, Phys Rev, 176 (1968) 95 J L Gardner and J A R Samson, J EIectron Spectrosc Relat Phenom , 8 (1976) 469 J A R Samson, G N Haddad and J L Gardner, J Phys B, 10 (1977) 1749 W H Hancock and J A R Samson, J Electron Spectrosc Relat Phenom , 9 (1976) 211 M J van der Wlel, W Stoll, A Hamnett and C E Brlon, Chem Phys Lett , 37 (1976) 240 C E Brlon, A Hamnett, G R Wlght and M J van der Wlel, J Electron Spectrosc Relat Phenom , 12 (1977) 323
Phenom
2 3 4 5 6 7
190
8 9 10
K H Tan, C E Bnon, Ph E van der Leeuw and M van der Wlel, Chem Phys , 29 (1978) 299 J B West and G V Marr, Proc R Sot London, Ser A, 349 (1976) 397 E W Plummer, T Gustafsson, W Gudat and D E Eastman, Phys Rev A, 15 (1977) 2339
Spectroscopy
and Related
Phenomena,
o Elsevler Screntlfx Pubhshmg Company, Amsterdam -
22 (1981) 187-190 Prmted m The Netherlands
Short commumcatlon
RE-MEASUREMENTS OF PARTIAL PHOTOIONIZATION CROSSSECTIONS OF CH,, , NH3 AND H2 0 AT 58 4 nm BY He(I) PHOTOELECTRON SPECTROSCOPY
Y ACHIBA,
T YAMAZAKI
and K KIMURA*
Institute of Applred Electncrty, Hokkaldo Molecular Science, Ukazakz (Japan)
Unluerszty,
Sapporo,
and Instztute
for
(First received 18 March 1980, m final form 9 September 1980)
Klmura et al [I] have previously described a gas-phase photoelectron method that uses a bmary mixture of a standard and a sample m order to obtsun partial photolonlzatlon cross-sections of molecules We have recently Improved this method w&h the ad of a mmlcomputer-based data-processmg system In this commurucatlon, we report some results of our re-measurements of dlfferentlal and partial photolonlzatlon cross-sections of CH4, NH3 and Hz 0 The steps of the process used here are shown m the form of a flowchart in
Fig 1 The dlfferentlal photoloruzatlon cross-section I, = du,/di2 for producmg photoelectrons wlthm the solid angle dS2 at an angle 8 for unpolarized light 1s theoretically related to the part& photoldnlzatlon cross-se&on q
Fig 1 A flowchart mdlcatmg the processes of determmatlon of dlfferentlal and partial photolomzatlon cross-sectlons of molecules * To whom Okazakl444,
correspondence Japan)
should
be addressed (Institute
for Molecular
Science,
188
for producing I,(e)
a specific lonlc state by the expression
= (0,/47r){l-
@,/4)(3
[l]
cos2e - 1))
where p, 1s the asymmetry parameter The He(I) photoelectron spectrometer used here 1s essentially the same as that used previously [ 11, photoelectron spectra being measured at 8 = 90” The mtensltles of the He(I) spectra were corrected for electron collection efficiency on the bans of the mtenslty data for N2, O2 and CO2 reported by Gardner and Samson [3] Relative band mtensltles obtained with respect to the standard were then converted to absolute 1, (90) values on the basis of a reference value of 0 78 Mb for I1=1 (90) of N, derived from eqn (1) using the values 0, =1 = 8 4 Mb and 0, =1 = 0 68 previously reported by Samson et al [4, 51 The features which we have improved for the present photoelectron intensity measurements are the followmg (1) The mole fraction of the sample m each binary mixture introduced mto the lonlzatlon chamber of the spectrometer via a needle valve, was determined by using two vacuum gauges of different types (Baratron and Pram gauges) Previously, it was assumed that the moIe fraction of the sample m the lomzatlon area 1s the same as that m the mltlal gas reservoir In the present study N, was used as a standard for the intensity measurements on both CH4 and NH3, and the mole fractions m the loruzatlon area were carefully determined by analyzing the Baratron and Plranr outputs For HZO, however, we used NH3 as a standard, without any mole fraction correction, since the Plranl gauge used was unstable for H2 0 vapour (For a m&ure of Hz0 and NH3, the mole fraction correction IS probably within 3% ) (2) The number of data sampled durmg photoelectron intensity measurements as well as pressure measurements was much increased by the use of a mmlcomputer (Model YHP 2105A), and the reproduclblhty of the data was repeatedly checked Results obtamed here for 1, (90) and o, of CH4, NH, and H, 0 are summarized m Table 1, and compared with our previous results as well as the electron-impact data on o, reported by Brlon et al [6-81 From Table 1 It can be seen that there are no maJor discrepancies between the three sets of data except for the 2B2 state of H20+ for which much larger values are obtamed m the present study The reason for this 1s uncertain, but one of the reasons may be that the standard devlatlon introduced m the transmlsslon correction above 19 eV IS much larger than that below 19 eV It should be pointed out that care must be taken especially for intensity measurements of low-energy photoelectrons In the present study, only the He(I) 58 4 nm lme was used It IS well known that synchrotron radiation 1s a very useful source for studying a, and @, as a function of photon energy over a wide energy range [ 9, lo]
189
TABLE
1
DIFFERENTIAL AND PARTIAL CH4, NH3 and Hz 0 AT 58 4 nm Molecule
Iomc state
PHOTOIONIZATION
This work
CROSS-SECTIONS
OF
Previous work [ 1 ]
Brlon et al [6-S]
I,(901
4
1,(90)
4
4
(334
T2
3 11
33 9
2 95
32 2
31 1
NH3
Al El
0 63 1 94
65 23 1
0 78 199
81 23 7
57 22 9
Hz0
B1 Al
0 71 0 72 1 14
71 85 14 8
0 59 0 51 0 65
59 60 84
62 58
B2
(Mb)
The present method can, of course, be apphed for synchrotron radratlon The advantage of the present method m usmg a binary gaseous mixture 1s that partial photolonlzatlon cross-sections can be obtamed from measurements of onIy photoelectron mtenslty using a conventional photoelectron spectrometer As already pomted out by Gardner and Samson [3], It 1s desirable to carry out direct photoelectron measurements at the magic angle of 54”44’ rather than at 90”
ACKNOWLEDGEMENT
The authors wish to thank Mr Y Shmdo for his expert advlce on the construction of the data-processmg system
REFERENCES 1
K Klmura, Y Achlba, M Momshlta and T Yamazakr, J Electron Spectrosc Relat , 15 (1979) 269 J C Tully, B S Berry and B J Dalton, Phys Rev, 176 (1968) 95 J L Gardner and J A R Samson, J EIectron Spectrosc Relat Phenom , 8 (1976) 469 J A R Samson, G N Haddad and J L Gardner, J Phys B, 10 (1977) 1749 W H Hancock and J A R Samson, J Electron Spectrosc Relat Phenom , 9 (1976) 211 M J van der Wlel, W Stoll, A Hamnett and C E Brlon, Chem Phys Lett , 37 (1976) 240 C E Brlon, A Hamnett, G R Wlght and M J van der Wlel, J Electron Spectrosc Relat Phenom , 12 (1977) 323
Phenom
2 3 4 5 6 7
190
8 9 10
K H Tan, C E Bnon, Ph E van der Leeuw and M van der Wlel, Chem Phys , 29 (1978) 299 J B West and G V Marr, Proc R Sot London, Ser A, 349 (1976) 397 E W Plummer, T Gustafsson, W Gudat and D E Eastman, Phys Rev A, 15 (1977) 2339