4.2. Site Data

Surface-phase species exist on sites, and a site and its species must be identified on one or more lines of site data. The first line in a set of site data must start with the word SITE ; an optional name may be associated with a site if it immediately follows SITE and is delimited by slashes(/). If no name for the site is supplied, a default name SITE n is provided, where n is the number of a site (for example, SITE2 for the second site type listed). Following SITE and/or the site name, the word SDEN and a slash-delimited density (the standard state site density for this site, in mole/cm2) for the site is required.

The optional keyword INTERFACE can be used to specify the phases (homogeneous phases such as the gas phase and the bulk phases) that share the surface site phase (see the example in Figure 4.2: Examples of Site Data ). The INTERFACE keyword is slash (/)-limited and must follow immediately after the SDEN keyword. A list of at least one but no more than two interfacing phases can be assigned to a surface site phase. The first phase of the list is the primary neighbor phase; if the temperature of the surface site phase is not given explicitly, the temperature of the primary neighbor phase will be assigned to the site phase. The INTERFACE keyword is utilized only by the multiphase reactor models. The species that can reside on the site type are declared by a list of species symbols (names) on the same line or on additional lines.

Note:  The name of a site species must not duplicate the name of a gas-phase species or a bulk species, and must be unique among the site species for all materials.

An optional slash-delimited site occupancy number may follow a species name, that is, the number of individual sites that this species occupies. (For example, a large chemical species might cover two or more sites.) The default site occupancy for a surface species is 1. The sets of SITE data input can continue for as many site types as are needed.

Any set of up to sixteen upper- or lower-case characters can be used as a site name or species symbol. In addition, each species must be composed of elements that have been identified in the Gas-phase Kinetics Pre-processor and thus contained in the Gas-phase Kinetics Linking File. One of the purposes of the site data is to define the order in which arrays of site species information are referenced in the Surface Kinetics Subroutine Library.

Note:  Species symbols may not begin with a number, a plus sign (+), a pound sign (#), or an equality sign (=), have imbedded blanks, or include a slash (/). An ionic species may end with any number of plus or minus signs; an imbedded plus sign must be enclosed in parentheses.

Any line starting with or any portion of a line following an exclamation mark (!) is considered a comment and will be ignored. Blank lines are also ignored. Figure 4.2: Examples of Site Data shows sample site data. The rules for site data are summarized in Table 4.1: Summary of the Rules for Site Data .

For multiphase chemistry, sites can be defined for the liquid surface using the same format used for the solid surface, as described in the preceding paragraphs.

Figure 4.2: Examples of Site Data

SITE / PLANE /               SDEN/1.04E-9/   ! PLANAR SITE
	 ASH(V)                                      ! FIRST SPECIES ON PLANE SITE
 ASH2(V) ASH3(V) H(S) CH3(V) AS(V) AS2(V)/2/
 V                                           ! EMPTY PLANAR SITE
END                                          ! AN END STATEMENT IS OPTIONAL
SITE / LEDGE /   SDEN/1.66E-10/              ! LEDGE SITE
  GACH(L)                                    ! FIRST SPECIES ON LEDGE
  DMG(L)/2/                                  ! THIS SPECIES OCCUPIES 2 SITES
  L                                          ! EMPTY LEDGE SITE
SITE	SDEN/1.0E-10/ GA(S)                      ! SITE WITH ONLY ONE SPECIES
                                               ! SITE NAME NOT INCLUDED


SITE/ANODE_GAS/ SDEN/0.00004062194/  INTERFACE/ANODE Gas/   ! INERFACE SITE SPECIFIED
                                                            ! SITE "ANODE_GAS" IS THE INTERFACE 
                                                            ! BETWEEN THE BULK PHASE "ANODE" AND
                                                            ! THE "Gas" PHASE 
H(*)/1/   
PT(*)/1/ 
END

BULK /ANODE/
PT(B)
END

Table 4.1: Summary of the Rules for Site Data

Rule

Description

1

Site data must start with a line containing the word SITE, followed by an optional slash-delimited name (that is, SITE/ name /).

2

The standard state site density is required as a slash-delimited number (in mole/cm2) following the word SITE and/or the site name, and preceded by the word SDEN.

3

The site density is followed by one or more site species name declarations. Declaring a site with no site species is an error.

4

Site and species names are composed of up to sixteen upper- or lower-case character symbols. The names cannot begin with the characters +, =, #, or a number; an ionic species name may end with one or more + or - signs; an embedded plus sign must be enclosed in parentheses (+). Names cannot include a slash (/).

5

All species names should be unique; duplicate species names will be ignored and a warning issued. A species name may not duplicate a name of a gas-phase species, another surface species, or a bulk species.

6

A site name must not duplicate the name of any other phase (gas, surface site, or bulk phase).

7

Each surface species that subsequently appears in a surface reaction must have been declared in this section.

8

A site species name may appear anywhere on the line.

9

A site species may have a slash-delimited site occupancy (the number of sites that this species occupies on the surface) following the species name.

10

A species name declaration that begins on one line may not continue to the next line (that is, do not break a species name into two lines).

11

There may be more than one set of SITE data.

12

All characters on a line following an exclamation mark are considered comments.

13

SITE data are not required.