Subject: VERTICAL AND ADIABATIC IONIZATION ENERGY--REPLIES;THANKS

From: "E. Lewars" <[email-masked]>
Date: Mon, 19 Jul 1999 11:29:49 -0400 (EDT)

1999 July 19

  REPLIES TO QUESTION ABOUT VERTICAL AND ADIABATIC IONIZATION POTENTIALS

Hello,
Here are the responses to my question.

I wish to thank all who responded.

There is plenty of info' on IPs and EAs (reply #2, 4 ), but it not always stated
explicitly if the measured quantity is a vertical or adiabatic energy. I gather
that the data normally published are for adiabatic IPs and EAs. It seems that if
you want vertical quantities you have to ferret them out of the literature.

    E. Lewars

--------------------
THE QUESTION:

1999 July 11

      SOME IONIZATION POTENTIALS (AND IF POSSIBLE ELECTRON AFFINITIES)

Hello,

Has anyone *experimental* values (with references) for vertical _and_
adiabatic ionization potentials of a few molecules:

    molecule A:    vert IP   adiabatic IP
    molecule B:    vert IP   adiabatic IP
    molecule C:    vert IP   adiabatic IP

  I'm looking for the IPs (ionization energies; the minimum  E needed to ionize
the molecule) of fairly small molecules, say 2--8 heavy (non-H) atoms.

 (If the same info is also available on the _electron affinities_ of a few
molecules, I would appreciate receiving this too).

     Thanks,
       E. Lewars
==========================
THE REPLIES:

#1
Date: Mon, 12 Jul 1999 10:58:04 +0300 (EET DST)
To: "E. Lewars" <[email-masked]>
Subject: Re: CCL:VERTICAL & ADIABATIC IONIZATION POT
Message-ID: <[email-masked]>

Dear Dr. Lewars,

I would appreciate if you summarized for the group any responses you may
receive. This is very interesting data.

Regards,
John Kerkines
Athens, Grece
==========

#2
  N  3   Jul 12 Karl Irikura       (94)   Re: CCL:VERTICAL & ADIABATIC IONIZACommand: Read MessageMessage 3/6 from Karl Irikura                            Jul 12 '99 at 9:16 am

X-Sender: [email-masked]
Date: Mon, 12 Jul 1999 09:16:26 -0400
To: "E. Lewars" <[email-masked]>
Subject: Re: CCL:VERTICAL & ADIABATIC IONIZATION POT
Mime-Version: 1.0

Dear Dr. Lewars,

I'm not aware of any complilations of vertical IPs.  But many
adiabatic values are available online from the NIST WebBook:
http://webbook.nist.gov/  It includes many references.  If you check
those that involve measured photoelectron spectra, the original
papers may contain vertical IPs, either tabulated or in the
experimental spectra.

Many adiabatic EAs are also compiled in the WebBook, and the
corresponding references to PES experiments may provide vertical
detachment energies (viz., at the geometry of the anion).  But I'm
not sure how one could easily measure vertical electron affinities
(viz., at the geometry of the neutral molecule).  The only way I can
think of would be to have a complete vibrational assignment of the
anion photoelectron spectrum and find the most intense peak that has
as its upper state the vibrational ground state of the neutral.
Please let me know if you learn of a better way!

Sincerely,

Karl Irikura

----------------------------------------------
Dr. Karl K. Irikura
National Institute of Standards and Technology
100 Bureau Drive, Stop 8380
Gaithersburg, MD  20899-8380
voice: 301-975-2510     fax: 301-869-4020
e-mail: [email-masked]
http://www.nist.gov/compchem/
----------------------------------------------

#3
  N  4   Jul 12 Matthew F Schlecht (69)   Re: CCL:VERTICAL & ADIABATIC IONIZACommand: Read MessageMessage 4/6 from Matthew F Schlecht                      Jul 12 '99 at 2:00 pm
X-Lotus-FromDomain: DUPONT@DUPONT_MHUB
To: "E. Lewars" <[email-masked]>
Date: Mon, 12 Jul 1999 14:00:24 -0400
Subject: Re: CCL:VERTICAL & ADIABATIC IONIZATION POT

Prof. Lewars,

     I would be very interested in seeing the responses to your question.
     I'm assuming that you are exploring ways to model these properties
computationally, and if you are willing I'd be very interested in hearing
more about that as well.
     I hope you will post your usual informative summary to the CCL.

                             Matthew Schlecht

                                 DuPont Ag

 [Thanks. Yes, I want to calculate a few IPs and EAs by different methods and
to compare the results with experiment and with Koopmans theorem predictions.
   E. Lewars ]

============

#4
           Jul 19 Karl Irikura       (161)  Re: IONIZATION ECommand: Read MessageMessage 4/4 from Karl Irikura

To: "E. Lewars" <[email-masked]>
Subject: Re: IONIZATION E

Dear Dr. Lewars,

There is no difference between the terms "ionization potential" (IP) and
"ionization energy" (IE).  Yes, the usual default is for values to be
adiabatic, since these are the thermodynamically relevant quantities, such
as measured by mass spectrometry.  Vertical quantities are usually
accessible only using spectroscopic methods, which are governed by
Franck-Condon factors.  As a result, adiabatic values are always <=
vertical values for endoergic quantities (such as IEs and electron
detachment energies), and are always >= vertical values for exoergic
quantities (such as electron affinities).  (This may be clearer if you
draw a diagram for a diatomic molecule.)

If you will work with ion thermochemistry, I recommend reading the
introduction to the GIANT tables for a reasonably brief review of the
techniques and pitfalls (esp. different thermodynamic conventions):  Lias,
S. G.; Bartmess, J. E.; Liebman, J. F.; Holmes, J. L.; Levin, R. D.;
Mallard, W. G. J. Phys. Chem. Ref. Data 1988, 17, Suppl. 1.  Similar
material appears to be online at http://webbook.nist.gov/chemistry/ion/
(but I haven't read this).

Best wishes!

Karl I.

At 09:30 PM 7/17/99 -0400, you wrote:
>1999 July 17
>Hello,
>
>Thank you for the information about ionization potentials on the NIST
>website. I gather from your email letter that ionization potential/energy
>(what is the difference between IP and IE anyway?) means _adiabatic_ 
>unless
>vertical is specifically stated. I thought that IP was sometimes 
>measured by mass spectrometry (the appearance potential, the minimum energy of
>electrons needed to ionize the molecule), and that in that case the ion was
>formed with the geometry of the neutral, giving the vertical IP.
>And it seems that for electron affinities, even more than for IPs, the
>standard measured values are adiabatic. No, I can't think of any other
way to get vertical EAs.

>It just occurs to me I'd better reread Chapter 10 in the book edited 
>by you and Frurip, especially the refs for p. 192.
>
>Thanks for your help
>
>   E. Lewars
>=======================

----------------------------------------------
Dr. Karl K. Irikura
National Institute of Standards and Technology
100 Bureau Drive, Stop 8380
Gaithersburg, MD  20899-8380
voice: 301-975-2510     fax: 301-869-4020
e-mail: [email-masked]
http://www.nist.gov/compchem/
----------------------------------------------