2 ) Real Time Clock (RTC). The RTC is used topruvide timing for the AID conversions. Our RTC is made bv Mountain Hardware. lnc.
interval as small as 0.1 ms.
3) Parallel Printer Interface Board (made by Apple, Inc.). This board is used to interface to our system printer. 4 ) High Speed Serial Interface Board (made by Apple, lne.). This board can be used as a printer interface for serial terminals, e.g., an LA-120 Decwriter, or printers. It can also be used fur high speed (9600 R a l ~ d dntn l tmnifer.
..
data analysis, e.g., curve deconvolution. fi) IDS 440 i"Paoer . . Tiger") Printer. This orinter allows us to make &gram andlor data listings,bur printer also has the graphics option with which we can make a cmnplete copy of the graphics screen, thus giving us a hard copy of our acquired spectra. 7) Black and white monitor used for graphics and program display. 8 ) Apple Graphics Tablet. The Graphics Tablet is used todigitize spectra from instruments not directly interfaced to the LDS. This allows us to easily enter data into the computer for further manipulation. The tablet is also used for preparing slides. The LDS was interfaced to an Hitachi UV-Visible spectrophotometer via the recorder outputs of the Hitachi. The voltage output from the Hitachi is linear with absorbance in the range 0-2.0, i.e., 1.0 V corresponds to a 1.0 absorbance. The ADC input range is 0-5.0 V, i.e. 0 V = 0 and 5.0 V = 255. Therefore, the spectrometer output had to be amplified, via an operational amplifier circuit, to match the input requirements of the ADC. The AID conversions are accomplished (in BASIC) by a two instruction sequence. First, the particular AID channel number is put into the appropriate memory location via a POKE statement. This initiates the analog to digital conversion wrocess. Then the resultant value is read from another memory location using a PEEK statement. Because of the slow execution time of the POKE statement (10-15 ms.) the AID conversion process is finished by the time the PEEK statement is executed. The sampling rate of the ADC board is timed by using the RTC. There are several ways to accomd i s h this timing. The sim~lestmethod is to read the RTC and determine if it;s time totake a sample. This method is slow and is useful only for a low sampling rate ( ~ + 0 D and O ore the donor and +
m m
mih
(1,
(2) (3) respectlvrly.
Figure I. A ponion of a poster prepared on the 9872A plofter.Printing, including all special characters. was done with a single pass. Volume 58
Number 9
September 1981
69 1
derlining are supported. The operator can adjust top and left margins, pen color, plotting speed, character height, and aspect ratio (heightlwidth ratio), character slant, and line spacing. Once these parameters are selected, the program will proceed to plot the previously prepared text file. Text can be entered either from the keyboard just before plotting or fetched from prerecorded tape files. In either case the powerful 9825A editor simnlifies text nrevaration and error correction. A repeat featire allows t i e page to be marked over aeain if it is not dark enourh - or allows additional copies to be made. If non-standard characters are desired, the delimiter "I" is embedded in the text string to denote that a special character will follow; this nearly douhles the numher of keyboard characters. On encountering a "I" the program checks the next character to determine what special function must be invoked. If the special function requested is a printable character or simple operation, the character need only be defined through the plotter's user-defined character instruction. Additional special characters or functions are readily added to the dispatch table. Our special characters are: a carriage return and line feed ([C),and N (la), a (:-), a 9({0),a v(iv), a f (I#), a F (I$), a hack space (IB),and a I ( I I). Other special control characters include: the underline (I-) with its terninator (&), the superscript mode (IU) with its terminator (In), and the subscript mode (ID) with its terminator (Id). The repeat function (IS) terminates a page. The repeat function "IS" is placed in the text string to indicate the end of each page of text. On encountering "IS" the computer moves the pen to the side and asks the user if the page is to he repeated. If answered in the affirmative, the plot narameters are reset to the initial values and the entire . Daee is replotted. This process is repeated until the operator anvaee swers in the neeative. If the . .. is not to be repeated, the d o t parameters for the next page are set up in a dialog. For unanswered questions the previous page's parameters remain in effect. The super- ( J U )and suhscript ( { D )modes shift the print line up and down, respectively, and decrease the charac size for an appealing presentation. All special characters are functional during super- and suhscripting. and terminated either by Underlining is started by ' I-" "I-" or "IS". All characters ex underlining and subscrintine . piaced bekween the underline delimiters will be underlined. Carriage return line feeds do not terminate underlining. The current program is written in Hewlett-Packard's Basic-like HPL lanrnaee for an H P 9825A calculator. It requires the plotter-~dvanced110, Advanced Programming and String KOM's. A program listing is available by sending a self-addressed stamped envelope to J. N. Demas a t the above address. The program can be copied by sending a carefully packed, new, certified cassette tape and $3.00 to .J. N. Demas. We gratefullv acknowledee sunvort bv the Air Force Office of Scientific ~ k s e a r c h(78:3596)and the donors of the Petroleum Research Fund, administered by the American Chemical Society.
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A Simple Hiickel Molecular Orbital Computer Program Written in BASIC for Microcomputer Use Barrie M. Peake and Roger Grauwmeijer Unversity of Otago P.0 Box 56 Duned~n,New Zeaiand The Simple Hiickel Molecular Orhital (SHMO) method is now included in most senior undergraduatelgraduate courses in quantum chemistry or theoretical organic chemistry. Hand 692
Journal of Chemical Education
calculations using this method are instructive hut limited due to the difficulty in solving the secular determinant for anything much more complicated than five-atom 71 framework (unless svmmetrv is used to block the determinant). Hence taining a large numher of atoms including heteioatoms. T o the best of our knowledae those that have heen published with one exception, viz. a p r o & n for an HP-25 calc;la(nr ( 4 ) ,have all been for execution on mainframe or minicomputers. The wide availability and acceptance of microcomputers in Chemistry Departments has been documented in previous ~ o m p u t e series r articles, and it became apparent to us that there was a real need for a SHMO program which would run on a variety of common microcomputers. We wish to report just such a program (HUCKELIBASIC) which we have written in the BASIC language for execution either on a Motorola 6800 Polyvalent System, Cumpucolor I1 or Apple I1 microcumouter all with 16 K of random access memurv two-dimensional arrays. The nroeram is based on the FORTRAN IV SHMO vrogram d k ~ c ~ i b eind a recent quantum chemistry text ( 5 ) a n d originally designed to be executed on an IBM 360 system. The input is simple and is prompted by questions within the program. It is currently dimensioned to handle up to 15 atoms (including heteroatoms) but this can he easily changed throuah alteration of a DIM statement. It calculates eneraies, molecdar orbital coefficients, bond orders, electron densities and polarizabilities for homonuclear and heteronuclear conjugated molecules, and bond lengths and free valences for homonuclear systems. Execution times for HUCKELBASIC on anv of the above for a complete calculation on benzene took 15 min on the Motorola 6800 Polwalent svstem. 1.50 min on the Comnucolor I1 and 1.3 mi; on the Apple 11. In spite of this we hive found from student use, that this increase in computation time is more than compensated for by the ready access and availahilitv of most denartmental comvuters toeether with immediate access to iutput. Further details and listings of the various versions of this program are availahle from the authors. Please specify which version, and in order to cover postage and printing costs send a check or money order for $5 (U.S. or New Zealand currency) made out to B.M. Peake, Chemistry Department, University of Otago, P.O. Box 56, Dunedin, New Zealand.
PMR Spectroscopy on a PET Glenn E. Palmer University of Prince Edward island Charlottetown. P.E.I. Canada C I A 4P3 The nrocess of develovine . " the ahilitv to interoret PMR spectra can be divided into discrete learning stages. In the first of these, the student must learn to recoenize with alacritv the e in a p3rticul:rr region t y p ~,,iprd.m which p r o ~ ~ u ac iy1131
