Subject: Re: CCL:Gaussian98-units of IR intensities

From: "Jens Spanget-Larsen" <[email-masked]>
Date: Thu, 14 Mar 2002 16:30:43 +0100

Marcin Makowski:

> I cannot guess what are KM/mole units used by Gaussian98 for IR
> intensities. I would be grateful if somebody could help me with
> that.

Dear Marcin:

In vibrational spectroscopy, integrated band intensity is usually 
defined by

A = (1/C) Integral,

where C is the concentration in mol/L = mol/(1000 cm^3) and the 
integral is over the absorption coefficient a(nu) as a function of 
wavenumber nu (the quantity a(nu)/C is frequently called the 
absorptivity). The absorption coefficient a(nu) is related to the 
decadic molar extinction coefficient eps(nu) through the relation  
a(nu) = ln(10) eps(nu) C, and has traditionally the units cm^(-1). 
Also wavenumbers are traditionally given in units of cm^(-1) and the 
integral thus produces a quantity in the units cm^(-2). Finally, 
multiplication with 1/C yields a result in the units 

(L/mol) cm^(-2) = (1000 cm^3/mol) cm(^-2) = 1000 cm/mol = 10 m/mol

However, chemists prefer the units 1000 m/mol = km/mol.

OK?

Yours, Jens >--<

NB! Please note new mail address: <[email-masked]>
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
JENS SPANGET-LARSEN         Office:         +45 4674 2710
Department of Chemistry     Fax:            +45 4674 3011
Roskilde University (RUC)   Mobile:         +45 2320 6246
P.O.Box 260                 E-Mail:        [email-masked]
DK-4000 Roskilde, Denmark   http://virgil.ruc.dk/~spanget
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=