FORM OF DEBENTURE

THE SECURITIES OFFERED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT
OF 1933, AS AMENDED, OR ANY STATE SECURITIES LAWS AND ARE BEING OFFERED AND SOLD
IN RELIANCE ON EXEMPTIONS FROM THE REGISTRATION REQUIREMENTS OF SUCH LAWS. THE
SECURITIES ARE SUBJECT TO RESTRICTIONS OF TRANSFERABILITY AND RESALE AND MAY NOT
BE TRANSFERRED OR RESOLD EXCEPT AS PERMITTED UNDER SUCH LAWS PURSUANT TO
REGISTRATION OR AN EXEMPTION THEREFROM. THE SECURITIES HAVE NOT BEEN APPROVED OR
DISAPPROVED BY THE SECURITIES AND EXCHANGE COMMISSION OR ANY OTHER REGULATORY
AUTHORITY, NOR HAVE ANY OF THE FOREGOING AUTHORITIES PASSED UPON OR ENDORSED THE
MERITS OF THIS OFFERING OR THE ACCURACY OR ADEQUACY OF THE OFFERING MATERIALS.
ANY REPRESENTATION TO THE CONTRARY IS UNLAWFUL.

CONVERTIBLE DEBENTURE DUE                 January    , 1998
                                          January    , 2000
$
Number      JAN -1998-101

      FOR VALUE RECEIVED, CELERITY SYSTEMS, INC., a New York corporation (the
      "Company"), hereby promises to pay _______________________________ or
      registered assigns (the "Holder") on January 2000, (the "Maturity Date"),
      the principal amount of __________HUNDRED THOUSAND Dollars ($ 00,000)
      U.S., and to pay interest on the principal amount hereof, in such amounts,
      at such times and on such terms and conditions as are specified herein.

Article 1. Interest

      The Company shall pay interest on the unpaid principal amount of this
Debenture (the "Debenture") at the rate of Nine Percent (9.0%) per year, payable
at the time of each conversion until the principal amount hereof is paid in full
or has been converted. Interest shall be computed on the basis of a 360 day year
of 12, 30 day months. Each payment shall be paid in cash or in freely trading
Common Stock of the Company, at the Company's option. If paid in Common Stock,
the number of shares of the Company's Common Stock to be received shall be
determined by dividing the dollar amount of the interest by the then applicable
Conversion Price as of the interest payment date. "Conversion Price" shall mean
the lesser of (a) 75% of the 5-day average closing bid prices, as reported by
Bloomberg, LP for the five (5)


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consecutive trading days immediately preceding the Conversion Date (as
hereinafter defined) or (b) four (4) times the 5-day average closing bid prices,
as reported by Bloomberg, LP for the five (5) consecutive trading days
immediately preceding the Closing Date (as hereinafter defined). If the interest
is to be paid in cash, the Company shall make such payment within 5 business
days of the date of conversion. If the interest is to be paid in Common Stock,
said Common Stock shall be delivered to the Holder, or per Holder's
instructions, within 8 business days of the date of conversion. The Debentures
are subject to automatic conversion at the end of two years from the date of
issuance at which time all Debentures outstanding will be automatically
converted based upon the formula set forth in Section 3.2. The closing shall be
deemed to have occurred on the date the funds are received by the Company or its
Counsel (the "Closing Date").

Article 2. Method of Payment

      This Debenture must be surrendered to the Company in order for the Holder
to receive payment of the principal amount hereof. The Company shall have the
option of paying the interest on this Debenture in United States dollars or in
common stock upon conversion pursuant to Article 1 hereof. The Company may draw
a check for the payment of interest to the order of the Holder of this Debenture
and mail it to the Holder's address as shown on the Register (as defined in
Section 7.2 below). Interest and principal payments shall be subject to
withholding under applicable United States Federal Internal Revenue Service
Regulations.

Article 3. Conversion

      Section 3.1. Conversion Privilege

      (a) The Holder of this Debenture shall have the right, at its option, to
convert it into shares of common stock, par value $0.001 per share, of the
Company ("Common Stock") at any time ninety (90) calendar days following the
Closing Date and which is before the close of business on the Maturity Date,
except as set forth in Section 3.1(c) below. The number of shares of Common
Stock issuable upon the conversion of this Debenture is determined pursuant to
Section 3.2 and rounding the result to the nearest whole share.

      (b) Less than all of the principal amount of this Debenture may be
converted into Common Stock if the portion converted is $5,000 or a whole
multiple of $5,000 and the provisions of this Article 3 that apply to the
conversion of all of the Debenture shall also apply to the conversion of a
portion of it. This Debenture may not be converted, whether in whole or in part,
except in accordance with Article 3.

      (c) In the event all or any portion of this Debenture remains outstanding
on the second anniversary of the date hereof, the unconverted portion of such
Debenture will automatically be converted into shares of Common Stock on such
date in the manner set forth in Section 3.2.


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<PAGE>

      Section 3.2. Conversion Procedure.

      (a) Debentures. Upon receipt by the Company or its designated attorney of
a facsimile or original of Holder's signed Notice of Conversion followed by
receipt of the original Debenture to be converted in whole or in part in the
manner set forth in 3.2(b) below, the Company shall instruct its transfer agent
to issue one or more Certificates representing that number of shares of Common
Stock into which the Debenture is convertible in accordance with the provisions
regarding conversion set forth in Exhibit A hereto. The Seller's transfer agent
shall act as Registrar and shall maintain an appropriate ledger containing the
necessary information with respect to each Debenture.

      (b) Conversion Procedures. The face amount of this Debenture may be
converted anytime ninety (90) calendar days following the Closing Date. Such
conversion shall be effectuated by surrendering to the Company at its address
for notice pursuant to Article 8 hereof, this Debenture to be converted together
with a facsimile or original of the signed Notice of Conversion which evidences
Holder's intention to convert the Debenture indicated. The date on which the
Notice of Conversion is effective ("Conversion Date") shall be deemed to be the
date on which the Holder has delivered to the Company at its address for notice
pursuant to Section 10(c) of the Subscription Agreement a facsimile or original
of the signed Notice of Conversion. The original Debenture(s) to be converted
shall be delivered to the Company at such address within 3 business days
thereafter.

      (c) Common Stock to be Issued. Upon the conversion of any Debentures and
upon receipt by the Company of a facsimile or original of Holder's signed Notice
of Conversion Seller shall instruct Seller's transfer agent to issue Stock
Certificates without restrictive legend or stop transfer instructions, if at
that time the Registration Statement has been deemed effective (or with proper
restrictive legend if the Registration Statement has not as yet been declared
effective), in the name of Holder (or its nominee) and in such denominations to
be specified at conversion representing the number of shares of Common Stock
issuable upon such conversion, as applicable. The certificates shall be
delivered to the address specified in the Conversion Notice or, if no such
address is specified, to the address set forth pursuant to Section 10(c) of the
Subscription Agreement. Seller warrants that no instructions, other than these
instructions, have been given or will be given to the transfer agent and that
the Common Stock shall otherwise be freely transferable on the books and records
of Seller, except as may be set forth herein.

Notwithstanding any other provision contained herein, the parties agree that in
no event shall the Company be required to issue more than 19.99% of the number
of shares of Common Stock outstanding on the date of closing of the purchase and
sale of the Debentures upon the conversion of the Convertible Debentures, unless
the shareholders of the Company approve the issuance of additional Common Shares
or NASDAQ waives the requirement of Market Place Rule 4460(i)(1)(D). 


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The Company agrees to use commercially reasonable efforts to obtain such
approval or waiver on or prior to the 90th day following the date that more than
19.99% of the Common Stock is issuable by scheduling a shareholders meeting as
soon as practicable after the Closing Date. For every 30 day period following
such 90th day, the Company shall pay 1% liquidated damages until approval (or
waiver) is received. Such damages shall only be payable as long as more than
19.99% of the outstanding Common Stock is issuable.

The Company acknowledges that its failure to obtain said shareholder approval
within 90 days following the date that more than 19.99% of the Common Stock is
issuable will cause the Holder to suffer damages in an amount that will be
difficult to ascertain. Accordingly, the parties agree that it is appropriate to
include in this Agreement a provision for liquidated damages. The parties
acknowledge and agree that the liquidated damages provision set forth in this
section represents the parties' good faith effort to quantify such damages and,
as such, agree that the form and amount of such liquidated damages are
reasonable and will not constitute a penalty. The payment of liquidated damages
shall not relieve the Company from its obligations to deliver the Common Stock
pursuant to the terms of this Agreement.

      (d) (i) Conversion Rate. Holder is entitled, at its option to convert the
face amount of this Debenture, plus accrued interest on the portion of the
Debenture being converted, anytime beginning ninety (90) calendar days following
the Closing Date, at the Conversion Price as defined in Article 1 hereof. No
fractional shares or scrip representing fractions of shares will be issued on
conversion, but the number of shares issuable shall be rounded up or down, as
the case may be, to the nearest whole share. The Debentures are subject to a
mandatory, 24 month conversion feature at the end of which all Debentures
outstanding will be automatically converted, upon the terms set forth in this
section ("Mandatory Conversion Date").

      (e) Nothing contained in this Debenture shall be deemed to establish or
require the payment of interest to the Holder at a rate in excess of the maximum
rate permitted by governing law. In the event that the rate of interest required
to be paid exceeds the maximum rate permitted by governing law, the rate of
interest required to be paid thereunder shall be automatically reduced to the
maximum rate permitted under the governing law and such excess shall be returned
with reasonable promptness by the Holder to the Company.

      (f) It shall be the Company's responsibility to take all necessary actions
and to bear all such costs to issue the Certificate for the Common Stock
issuable upon conversion of the Debenture as provided herein, including the
responsibility and cost for delivery of an opinion letter to the transfer agent,
if so required. The person in whose name the certificate of Common Stock is to
be registered shall be treated as a shareholder of record on and after the
conversion date. Upon surrender of any Debentures that are to be converted in
part, the Company shall 


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issue to the Holder a new Debenture equal to the unconverted amount, if so
requested in writing by Holder.

      (g) Within eight (8) business days after receipt of the documentation
referred to above in Section 3.2(b), the Company shall deliver a certificate, in
accordance with Section 3.2(c) for the number of shares of Common Stock issuable
upon the conversion. It shall be the Company's responsibility to take all
necessary actions and to bear all such costs to issue the Common Stock as
provided herein, including the cost for delivery of an opinion letter to the
transfer agent, if so required. The person in whose name the certificate of
Common Stock is to be registered shall be treated as a shareholder of record on
and after the conversion date. Upon surrender of any Debentures that are to be
converted in part, the Company shall issue to the Holder a new Debenture equal
to the unconverted amount, if so requested in writing by Holder.

      In the event the Company does not make delivery of the Common Stock, as
instructed by Holder, within 8 business days after delivery of this original
Debenture, then in such event the Company shall pay to Holder an amount, in
cash, in immediately available funds or shares of Common Stock (calculated on
the basis of the Conversion Rate on such 8th business day), at the rate
applicable to the Conversion Default Payments set forth below until the date of
delivery of the Common Stock.

      The Company acknowledges that its failure to deliver the Common Stock
within 8 business days after receipt of the documentation referred to above in
Section 3.2(b) will cause the Holder to suffer damages in an amount that will be
difficult to ascertain. Accordingly, the parties agree that it is appropriate to
include in this Debenture a provision for liquidated damages. The parties
acknowledge and agree that the liquidated damages provision set forth in this
section represents the parties' good faith effort to qualify such damages and,
as such, agree that the form and amount of such liquidated damages are
reasonable and will not constitute a penalty. The payment of liquidated damages
shall not relieve the Company from its obligations to deliver the Common Stock
pursuant to the terms of this Debenture.

      To the extent that the failure of the Company to issue the Common Stock
pursuant to this Section 3.2(g) is due to the unavailability of authorized but
unissued shares of Common Stock, the provisions of this Section 3.2(g) shall not
apply but instead the provisions of Section 3.2(h) shall apply. In no event
shall the Company be required to make payments under both this Section 3.2(g)
and Section 3.2(h) with respect to any failure to issue or deliver certificates
representing Common Stock.

      The Company shall make any payments incurred under this Section 3.2(g) by
the fifth business day of the calendar month following the calendar month in
which such payment was incurred.


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<PAGE>

      (h) The Company shall at all times reserve and have available all Common
Stock necessary to meet conversion of the Debentures by all Holders of the
entire amount of Debentures then outstanding. If, at any time Holder submits a
Notice of Conversion and the Company does not have sufficient authorized but
unissued shares of Common Stock (or alternative shares of Common Stock as may be
contributed by stockholders) available to effect, in full, a conversion of the
Debentures (a "Conversion Default", the date of such default being referred to
herein as the "Conversion Default Date"), the Company shall issue to the Holder
all of the shares of Common Stock which are available, and the Notice of
Conversion as to any Debentures requested to be converted but not converted (the
"Unconverted Debentures"), upon Holder's sole option, may be deemed null and
void. The Company shall provide notice of such Conversion Default ("Notice of
Conversion Default") to all existing Holders of outstanding Debentures, by
facsimile, within three (3) business day of such default (with the original
delivered by overnight or two day courier), and the Holder shall give notice to
the Company by facsimile within five business days of receipt of the original
Notice of Conversion Default (with the original delivered by overnight or two
day courier) of its election to either nullify or confirm the Notice of
Conversion.

      The Company agrees to pay to all Holders of outstanding Debentures
payments for a Conversion Default ("Conversion Default Payments") in the amount
of (N/365) x (.24) x the initial issuance price of the outstanding and/or
tendered but not converted Debentures held by each Holder where N = the number
of days from the Conversion Default Date to the date (the "Authorization Date")
that the Company authorizes a sufficient number of shares of Common Stock to
effect conversion of all remaining Debentures. The Company shall send notice
("Authorization Notice") to each Holder of outstanding Debentures that
additional shares of Common Stock have been authorized, the Authorization Date
and the amount of Holder's accrued Conversion Default Payments. The accrued
Conversion Default shall be paid in cash or at the Company's option, in Common
Stock (at the Conversion Rate on the date of the Conversion Default) on or prior
to the fifth business day of the calendar month following the calendar month in
which the Conversion Default occurred and any subsequent calendar month in which
the Conversion Default is continuing.

      The Company acknowledges that its failure to maintain a sufficient number
of authorized but unissued shares of Common Stock to effect in full a conversion
of the Debentures will cause the Holder to suffer damages in an amount that will
be difficult to ascertain. Accordingly, the parties agree that it is appropriate
to include in this Agreement a provision for liquidated damages. The parties
acknowledge and agree that the liquidated damages provision set forth in this
section represents the parties' good faith effort to quantify such damages and,
as such, agree that the form and amount of such liquidated damages are
reasonable and will not constitute a penalty. The payment of liquidated damages


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<PAGE>

shall not relieve the Company from its obligations to deliver the Common Stock
pursuant to the terms of this Debenture.

            (i) The Holder is limited in the amount of this Debenture it may
convert and own. Other than the Mandatory Conversion provisions contained in
this Debenture which are not limited by the following, in no other event shall
the Holder be entitled to convert any amount of Debentures in excess of that
amount upon conversion of which the sum of (1) the number of shares of Common
Stock beneficially owned by the Holder and its affiliates (other than shares of
Common Stock which may be deemed beneficially owned through the ownership of the
unconverted portion of the Debenture), and (2) the number of shares of Common
Stock issuable upon the conversion of the Debentures with respect to which the
determination of this provision is being made, would result in beneficial
ownership by the Holder and its affiliates of more than 4.99% of the outstanding
shares of Common Stock of the Company (after taking into account the shares to
be issued to the Holder upon such conversion). For purposes of this provision to
the immediately preceding sentence, beneficial ownership shall be determined in
accordance with Section 13(d) of the Securities Exchange Act of 1934, as
amended, and Regulation 13 D-G thereunder, except as otherwise provided in
clause (1) of such provision. The Holder further agrees that if the Holder
transfers or assigns any of the Debentures to a party who or which would not be
considered such an affiliate, such assignment shall be made subject to the
transferees or assignees specific agreement to be bound by the provisions of
this Section as if such transferee or assignee were a signatory to the
Subscription Agreement.

      (j) Redemption. The Company reserves the right, at its sole option, to
call a mandatory redemption of any percentage of the balance on the Debentures
as follows: In the event the Company exercises such right of redemption up to
and including the 90th calendar day following the Closing Date, it shall pay the
Holder, in U.S. currency One Hundred Fifteen (115%) of the face amount of the
Debentures to be redeemed, plus accrued interest. In the event the Company
exercises such right of redemption at anytime during the 91st through the 180th
calendar day following the Closing Date it shall pay the Holder, in U.S.
currency One Hundred Twenty (120%) of the face amount of the Debentures to be
redeemed, plus accrued interest. In the event the Company exercises such right
of redemption at anytime during the 181st calendar day following the Closing
Date through the expiration of the two year conversion period it shall pay the
Holder, in U.S. currency One Hundred Twenty-five (125%) of the face amount of
the Debentures to be redeemed, plus accrued interest. The date by which the
Debentures must be delivered to the Escrow Agent shall not be later than 5
business days following the date the Company notifies Holder by facsimile of the
redemption. The Company shall give the Holder at least 5 business day's notice
of its intent to redeem.

      Section 3.3. Fractional Shares. The Company shall not issue fractional
shares of Common Stock, or scrip representing fractions of such shares, upon


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the conversion of this Debenture. Instead, the Company shall round up or down,
as the case may be, to the nearest whole share.

      Section 3.4. Taxes on Conversion. The Company shall pay any documentary,
stamp or similar issue tax due on the issue of shares of Common Stock upon the
conversion of this Debenture. However, the Holder shall pay any such tax which
is due because the shares are issued in a name other than its name.

      Section 3.5. Company to Reserve Stock. The Company shall reserve the
number of shares of Common Stock required pursuant to and upon the terms set
forth in Section 3(a) of the Subscription Agreement, to permit the conversion of
this Debenture subject to certain options granted to the Company and referred to
in Section 3(a) of the Subscription Agreement. All shares of Common Stock which
may be issued upon the conversion hereof shall upon issuance be validly issued,
fully paid and nonassessable and free from all taxes, liens and charges with
respect to the issuance thereof.

      Section 3.6. Restrictions on Transfer. This Debenture has not been
registered under the Securities Act of 1933, as amended, (the "Act") and is
being issued under Section 4(2) of the Act and Rule 506 of Regulation D
promulgated under the Act. This Debenture and the Common Stock issuable upon the
conversion thereof may only be offered or sold pursuant to registration under or
an exemption from the Act.

      Section 3.7. Mergers, Etc. If the Company merges or consolidates with
another corporation and the holders of the Common Stock are entitled to receive
stock, securities or property in respect of or in exchange for Common Stock,
then this Debenture shall automatically be converted into Common Stock upon the
terms and conditions set forth in this Article 3, except that the Conversion
Date shall be deemed to be the date of the consummation of the merger.
Thereafter the Holder shall be entitled to receive the kind and amount of stock,
securities or property receivable upon such merger or consolidation, as would
any other Common Stock holder of the Company.

Article 4. Mergers and Adjustments

      Section 4.1 Mergers. The Company shall not consolidate or merge into any
person, unless such person assume in writing the obligations of the Company
under this Debenture pursuant to Section 3.7. Any reference herein to the
Company shall refer to such surviving or transferee corporation and the
obligations of the Company shall terminate upon such written assumption.

      Section 4.2 Adjustments. The number of shares of Common Stock purchasable
upon the conversion of this Debenture shall be subject to adjustments as
follows:


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      (a) In case the Company shall (i) pay a dividend on Common Stock in Common
Stock or securities convertible into, exchangeable for or otherwise entitling a
holder thereof to receive Common Stock, (ii) declare a dividend payable in cash
on its Common Stock and at substantially the same time offer its shareholders a
right to purchase new Common Stock (or securities convertible into, exchangeable
for or other entitling a holder thereof to receive Common Stock) from the
proceeds of such dividend (all Common Stock so issued shall be deemed to have
been issued as a stock dividend), (iii) subdivide its outstanding shares of
Common Stock into a greater number of shares of Common Stock, (iv) combine its
outstanding shares of Common Stock into a smaller number of shares of Common
Stock, or (v) issue by reclassification, reorganization or recapitalization of
its Common Stock any shares of Common Stock or other securities of the Company,
the number of shares of Common Stock issuable upon conversion of this Debenture
immediately prior thereto shall be adjusted so that the Holder of this Debenture
shall be entitled to receive after the happening of any of the events described
above that number and kind of shares as the Holder would have received had this
Debenture been converted immediately prior to the happening of such event or any
record date with respect thereto. Any adjustment made pursuant to this
subdivision shall become effective immediately after the close of business on
the record date in the case of a stock dividend and shall become effective
immediately after the close of business on the effective date in the case of a
stock split, subdivision, combination or reclassification.

      (b) In case the Company shall distribute, without receiving consideration
therefor, to all holders of its Common Stock evidences of its indebtedness or
assets (excluding cash dividends other than as described in Section 4.2(a)), or
rights, options or warrants or convertible or exchangeable securities containing
the right to subscribe for or purchase shares of Common Stock, then in such
case, the number of shares of Common Stock thereafter issuable upon conversion
of this Debenture shall be determined by multiplying the number of shares of
Common Stock theretofore issuable upon conversion of this Debenture, by a
fraction, of which the numerator shall be the closing bid price per share of
Common Stock on the record date for such distribution, and of which the
denominator shall be the closing bid price of the Common Stock less the then
fair value (as determined by the Board of Directors of the Company, whose
determination shall be conclusive) of the portion of the assets or evidences of
indebtedness so distributed or of such subscription rights, options or warrants,
or of such convertible or exchangeable securities applicable to one share of
Common Stock. Such adjustment shall be made whenever any such distribution is
made and shall become effective immediately after the record date for the
determination of stockholders entitled to receive such distribution.

      (c) Any adjustment in the number of shares of Common Stock issuable
hereunder otherwise required to be made by this Section 4.2 will not have to be
adjusted if such adjustment would not require an increase or decrease in one


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percent (1%) or more in the number of shares of Common Stock issuable upon
conversion of this Debenture. No adjustment in the number of shares of Common
Stock issuable upon conversion of this Debenture will be made for the issuance
of shares of capital stock to directors, employees or independent contractors
pursuant to the Company's or any of its subsidiaries' stock option, for the
purpose of the Company's Common Stock warrants issued, issuable or to be issued
for services rendered by others to the Company, stock ownership or other benefit
plans or arrangements or trusts related thereto or for issuance of any shares of
Common Stock pursuant to any plan providing for the reinvestment of dividends or
interest payable on securities of the Company and the investment of additional
optional amounts in shares of Common Stock under such plan.

Article 5. Reports

      The Company will mail to the Holder hereof at its address as shown on the
Register a copy of any annual, quarterly or other report or proxy statement that
it gives to its shareholders generally at the time such report or statement is
sent to shareholders.

Article 6. Defaults and Remedies

      Section 6.1. Events of Default. An "Event of Default" occurs if (a) the
Company does not make the payment of the principal of this Debenture when the
same becomes due and payable at maturity, upon redemption or otherwise, (b) the
Company does not make a payment, other than a payment of principal, for a period
of 5 business days thereafter, (c) the Company fails to comply with any of its
other agreements in this Debenture (other than any such failure to comply for
which liquidated damages are payable) and such failure continues for the period
and after the notice specified below, (d) the Company pursuant to or within the
meaning of any Bankruptcy Law (as hereinafter defined): (i) commences a
voluntary case; (ii) consents to the entry of an order for relief against it in
an involuntary case; (iii) consents to the appointment of a Custodian (as
hereinafter defined) of it or for all or substantially all of its property or
(iv) makes a general assignment for the benefit of its creditors or (v) a court
of competent jurisdiction enters an order or decree under any Bankruptcy Law
that: (A) is for relief against the Company in an involuntary case; (B) appoints
a Custodian of the Company or for all or substantially all of its property or
(C) orders the liquidation of the Company, and the order or decree remains
unstayed and in effect for 60 days, (e) the Company's Common Stock is no longer
listed on any recognized exchange including electronic over-the-counter bulletin
board. As used in this Section 6.1, the term "Bankruptcy Law" means Title 11 of
the United States Code or any similar federal or state law for the relief of
debtors. The term "Custodian" means any receiver, trustee, assignee, liquidator
or similar official under any Bankruptcy Law. A default under clause (c) above
is not an Event of Default until the holders of at least 25% of the aggregate
principal amount of the Debentures outstanding notify the Company of such
default and the Company does not cure it within fifteen (15) business days after
the receipt of such notice, which must 


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specify the default, demand that it be remedied and state that it is a "Notice
of Default".

      Section 6.2. Acceleration. If an Event of Default occurs and is
continuing, the Holder hereof by notice to the Company, may declare the
remaining principal amount of this Debenture to be due and payable. Upon such
declaration, the remaining principal amount shall be due and payable
immediately.

Article 7. Registered Debentures

      Section 7.1. Series. This Debenture is one of a numbered series of
Debentures which are identical except as to the principal amount and date of
issuance thereof and as to any restriction on the transfer thereof in order to
comply with the Securities Act of 1933 and the regulations of the Securities and
Exchange Commission promulgated thereunder. Such Debentures are referred to
herein collectively as the "Debentures". The Debentures shall be issued in whole
multiples of $5,000.

      Section 7.2. Record Ownership. The Company, or its attorney, shall
maintain a register of the holders of the Debentures (the "Register") showing
their names and addresses and the serial numbers and principal amounts of
Debentures issued to or transferred of record by them from time to time. The
Register may be maintained in electronic, magnetic or other computerized form.
The Company may treat the person named as the Holder of this Debenture in the
Register as the sole owner of this Debenture. The Holder of this Debenture is
the person exclusively entitled to receive payments of interest on this
Debenture, receive notifications with respect to this Debenture, convert it into
Common Stock and otherwise exercise all of the rights and powers as the absolute
owner hereof.

      Section 7.3. Registration of Transfer. Transfers of this Debenture may be
registered on the books of the Company maintained for such purpose pursuant to
Section 7.2 above (i.e., the Register). Subject to Section 3.6 above, transfers
shall be registered when this Debenture is presented to the Company with a
request to register the transfer hereof and the Debenture is duly endorsed by
the appropriate person, reasonable assurances are given that the endorsements
are genuine and effective, and the Company has received evidence satisfactory to
it that such transfer is rightful and in compliance with all applicable laws,
including tax laws and state and federal securities laws. When this Debenture is
presented for transfer and duly transferred hereunder, it shall be canceled and
a new Debenture showing the name of the transferee as the record holder thereof
shall be issued in lieu hereof. When this Debenture is presented to the Company
with a reasonable request to exchange it for an equal principal amount of
Debentures of other denominations, the Company shall make such exchange and
shall cancel this Debenture and issue in lieu thereof Debentures having a total
principal amount equal to this Debenture in such denominations as agreed to by
the Company and Holder.


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<PAGE>

      Section 7.4. Worn or Lost Debentures. If this Debenture becomes worn,
defaced or mutilated but is still substantially intact and recognizable, the
Company or its agent may issue a new Debenture in lieu hereof upon its
surrender. Where the Holder of this Debenture claims that the Debenture has been
lost, destroyed or wrongfully taken, the Company shall issue a new Debenture in
place of the original Debenture if the Holder so requests by written notice to
the Company actually received by the Company before it is notified that the
Debenture has been acquired by a bona fide purchaser and the Holder has
delivered to the Company an indemnity bond in such amount and issued by such
surety as the Company deems satisfactory together with an affidavit of the
Holder setting forth the facts concerning such loss, destruction or wrongful
taking and such other information in such form with such proof or verification
as the Company may request.

Article 8. Notices

      Any notice which is required or convenient under the terms of this
Debenture shall be duly given if it is in writing and delivered in person or
mailed by first class mail, postage prepaid and directed to the Holder of the
Debenture at its address as it appears on the Register or if to the Company, at
Celerity Systems, Inc., 1400 Centerpoint Boulevard, Knoxville, Tennessee 37932,
Attn: William R. Chambers, (p) 423-539-5300, (f) 423-539-3590 with a copy by
facsimile and mail to Kenneth R. Koch, Esq., Squadron, Ellenoff, Plesent &
Sheinfeld, LLP, 551 Fifth Avenue, New York, NY 10176 (p) 212-661-6500 (f)
212-697-6686. The time when such notice is sent shall be the time of the giving
of the notice.

Article 9. Time

      Where this Debenture authorizes or requires the payment of money or the
performance of a condition or obligation on a Saturday or Sunday or a public
holiday, or authorizes or requires the payment of money or the performance of a
condition or obligation within, before or after a period of time computed from a
certain date, and such period of time ends on a Saturday or a Sunday or a public
holiday, such payment may be made or condition or obligation performed on the
next succeeding business day, and if the period ends at a specified hour, such
payment may be made or condition performed, at or before the same hour of such
next succeeding business day, with the same force and effect as if made or
performed in accordance with the terms of this Debenture. A "business day" shall
mean a day on which the banks in New York are not required or allowed to be
closed.

Article 10. Waivers

      The holders of a majority in principal amount of the Debentures may waive
a default or rescind the declaration of an Event of Default and its consequences


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<PAGE>

except for a default in the payment of principal or conversion into Common
Stock.

Article 11. Rules of Construction

      In this Debenture, unless the context otherwise requires, words in the
singular number include the plural, and in the plural include the singular, and
words of the masculine gender include the feminine and the neuter, and when the
sense so indicates, words of the neuter gender may refer to any gender. The
numbers and titles of sections contained in the Debenture are inserted for
convenience of reference only, and they neither form a part of this Debenture
nor are they to be used in the construction or interpretation hereof. Wherever,
in this Debenture, a determination of the Company is required or allowed, such
determination shall be made by a majority of the Board of Directors of the
Company and if it is made in good faith, it shall be conclusive and binding upon
the Company and the Holder of this Debenture.

Article 12. Governing Law

      The validity, terms, performance and enforcement of this Debenture shall
be governed and construed by the provisions hereof and in accordance with the
laws of the State of Delaware applicable to agreements that are negotiated,
executed, delivered and performed solely in the State of Delaware.

Article 13. Litigation

      (a) Forum Selection and Consent to Jurisdiction. Any litigation based
thereon, or arising out of, under, or in connection with, this agreement or any
course of conduct, course of dealing, statements (whether oral or written) or
actions of the Company or Holder shall be brought and maintained exclusively in
the courts of the State of New York located in New York County. The Company
hereby expressly and irrevocably submits to the exclusive jurisdiction of the
state and federal courts of the State of New York located in New York County for
the purpose of any such litigation as set forth above and irrevocably agrees to
be bound by any final judgment rendered thereby in connection with such
litigation. The Company further irrevocably consents to the service of process
by registered mail, postage prepaid, or by personal service within or without
the State of New York. The Company hereby expressly and irrevocably waives, to
the fullest extent permitted by law, any objection which it may have or
hereafter may have to the laying of venue of any such litigation brought in any
such court referred to above and any claim that any such litigation has been
brought in any inconvenient forum. To the extent that the Company has or
hereafter may acquire any immunity from jurisdiction of any court or from any
legal process (whether through service or notice, attachment prior to judgment,
attachment in aid of execution or otherwise) with respect to itself or its
property, the Company hereby irrevocably waives such immunity in respect of its
obligations under this agreement and the other loan documents.


                                       13
<PAGE>

      (b) Waiver of Jury Trial. The Holder and the Company hereby knowingly,
voluntarily and intentionally waive any rights they may have to a trial by jury
in respect of any litigation based hereon, or arising out of, under, or in
connection with, this agreement, or any course of conduct, course of dealing,
statements (whether oral or written) or actions of the Holder or the Company.
The Company acknowledges and agrees that it has received full and sufficient
consideration for this provision and that this provision is a material
inducement for the Holder entering into this agreement.

      IN WITNESS WHEREOF, the Company has duly executed this Debenture as of the
date first written above.

                              CELERITY SYSTEMS, INC.


                              By_______________________________________
                                               its CEO  duly authorized


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<PAGE>

                                    Exhibit A

                              NOTICE OF CONVERSION

      (To be Executed by the Registered Holder in order to Convert the
Debentures.)

      The undersigned hereby irrevocably elects, as of ______________, 199_ to
convert $_________________ of the Debentures into Shares of Common Stock (the
"Shares") of CELERITY SYSTEMS, INC. (the "Company") according to the conditions
set forth in the Subscription Agreement dated _________________,1998.

Date of Conversion______________________________________________________________

Applicable Conversion Price_____________________________________________________

Number of Shares Issuable upon this conversion__________________________________

Signature_______________________________________________________________________
                  [Name]

Address_________________________________________________________________________

________________________________________________________________________________

Phone______________________   Fax_______________________________________________


                                       15
<PAGE>

                             Assignment of Debenture

        The undersigned hereby sell(s) and assign(s) and transfer(s) unto

________________________________________________________________________________
                   (name, address and SSN or EIN of assignee)

                                                  Dollars ($        )
________________________________________________________________________________
(principal amount of Debenture, $5,000 or integral multiples of $5,000)

of principal amount of this Debenture together with all accrued and unpaid
interest hereon.

Date:_____________Signed:_______________________________________________________
                            (Signature must conform in all
                            respects to name of Holder shown
                            of face of Debenture)

Signature Guaranteed:


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