Officers Certificate creating the 3.500% Senior Debentures due 2049 of Interstate Power and Light Company

“Reference Treasury Dealer” means each of (i) J.P. Morgan Securities LLC, (ii) Wells Fargo Securities, LLC and (iii) a primary treasury dealer selected by MUFG Securities Americas Inc., or their affiliates, which are primary United States government securities dealers and (iv) one other leading primary U.S. government securities dealer located in the United States (a “Primary Treasury Dealer”) reasonably selected by the Company, and such Primary Treasury Dealer’s successors that the Company specifies from time to time; provided, however, that if any of the foregoing or their affiliates cease to be a Primary Treasury Dealer, the Company will substitute therefor another Primary Treasury Dealer.

Unless this certificate is presented by an authorized representative of The Depository Trust Company, a New York corporation (“DTC”), to the Company (as defined below) or its agent for registration of transfer, exchange or payment, and any certificate issued is registered in the name of Cede & Co. or in such other name as is requested by an authorized representative of DTC (and any payment is made to Cede & Co. or to such other entity as is requested by an authorized representative of DTC), ANY TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL inasmuch as the registered owner hereof, Cede & Co., has an interest herein.

INTERSTATE POWER AND LIGHT COMPANY, a corporation duly organized and existing under the laws of the State of Iowa (herein called the “Company,” which term includes any successor Person under the Indenture hereinafter referred to), for value received, hereby promises to pay to Cede & Co., or registered assigns, the principal sum of THREE HUNDRED MILLION DOLLARS ($300,000,000) on September 30, 2049 and to pay interest on said principal sum from September 26, 2019, or from and including the most recent interest payment date to which interest has been paid or duly provided for, semi-annually, in arrears, on March 30 and September 30 of each year (each such date, an “Interest Payment Date”), commencing March 30, 2020 at the rate of 3.500% per annum to, excluding the date on which the principal hereof is paid or made available for payment. The amount of interest payable for any period will be computed on the basis of twelve 30-day months and a 360-day year. The interest so payable, and punctually paid or duly provided for, on any Interest Payment Date will, as provided in the Indenture, be paid to the Person in whose name this Debenture (or one or more Predecessor Securities, as defined in the Indenture) is registered at the close of business, on the Regular Record Date for such interest, which shall be the fifteenth calendar day before each Interest Payment Date. Any such interest installment not so punctually paid or duly provided for shall forthwith cease to be payable to the registered Holder on such Regular Record Date and may either be paid to the Person in whose name this Debenture (or one or more Predecessor Securities) is registered at the close of business on a Special

Record Date for the payment of such Defaulted Interest to be fixed by the Trustee, notice whereof shall be given to Holders of Debentures not later than 10 days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange on which the Debenture may be listed, or any book-entry system which may be applicable to this Debenture and upon such notice as may be required by such exchange or system, all as more fully provided in the Indenture.

Payment of the principal of and interest on any Debenture that is not a global Debenture will be made at the office or agency of the Company maintained for that purpose in The City of New York; provided, however, that at the option of the Company payment of interest may be made (i) by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register or (ii) by wire transfer in immediately available funds at such place and to such account as may be designated by the Person entitled thereto as specified in the Security Register. Payment of principal of and interest on any global Debenture will be made to DTC or its nominee, as the case may be, as the sole registered owner and the sole Holder of the global Debenture for all purposes under the Indenture. Payment of the principal of and interest on this Debenture will be made in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts.

Additional provisions of this Debenture are continued on the two pages following the execution and authentication of this Debenture and such provisions have the same effect as though fully set forth in this place.

Unless the certificate of authentication hereon has been executed by or on behalf of the Trustee by manual signature, this Debenture shall not be entitled to any benefit under the Indenture or be valid or obligatory for any purpose.

IN WITNESS WHEREOF, INTERSTATE POWER AND LIGHT COMPANY has caused this instrument to be duly executed under its corporate seal.

Dated: September 26, 2019

Name:    Barbara Tormaschy

Title:        Vice President and Treasurer

Attest:

_____________________________

Authorized Officer

This is one of the Debentures of the series designated herein referred to in the within‑mentioned Indenture.

as Trustee

Name:    

Title:    

This Debenture is one of a duly authorized issue of Debentures of the Company, designated as its “3.500% Senior Debentures due 2049” (herein called the “Debentures”), in aggregate principal amount of $300,000,000, issued under an Indenture, dated as of August 20, 2003 (herein called the “Indenture”), between the Company and The Bank of New York Mellon Trust Company, N.A., successor, as Trustee (the “Trustee”), to which Indenture and the Officer’s Certificate, dated September 26, 2019 (herein called the “Officer’s Certificate”), setting forth the terms and conditions of the Debentures, reference is hereby made for a statement of the respective rights, limitations of rights, duties and immunities thereunder of the Trustee, the Company and the Holders of the Debentures, and of the terms upon which the Debentures are, and are to be, authenticated and delivered.

At any time or from time to time prior to March 30, 2049 (the “Par Call Date”), the Debentures shall be redeemable at the option of the Company, in whole or in part, at a Redemption Price equal to the greater of (i) 100% of the principal amount of such Debentures and (ii) the sum, as determined by the Independent Investment Banker and delivered to the trustee, of the present values of the remaining scheduled payments of principal and interest thereon that would be due if the Debentures matured on the Par Call Date (exclusive of interest accrued to the Redemption Date) discounted to the Redemption Date on a semiannual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate plus 20 basis points, plus in each case accrued and unpaid interest to, but excluding, the Redemption Date. Notice of redemption will be given as provided in the Indenture to the Holder of the Debentures to be redeemed not less than 30 nor more than 60 days prior to the Redemption Date. At any time or after the Par Call Date, the Debentures shall be redeemable at the option of the Company, in whole or in part, at a Redemption Price equal to 100% of the principal amount of the Debentures being redeemed plus accrued and unpaid interest if any, to, but excluding, the Redemption Date.

If an Event of Default with respect to the Debentures shall occur and be continuing, the principal of the Debentures may be declared due and payable in the manner, with the effect and subject to the conditions, provided in the Indenture.

The Indenture contains provisions for satisfaction and discharge at any time of the entire indebtedness of this Debenture upon compliance by the Company with certain conditions set forth in the Indenture.

The Indenture contains provisions permitting the Company and the Trustee, with the consent of the Holders of not less than a majority in principal amount of the Outstanding Securities of all series affected, voting as one class, to modify the Indenture in a manner affecting the rights of the Holders of the Debentures; provided that no such modification may, without the consent of the Holder of each Outstanding Debenture, (i) change the Stated Maturity of, the principal of, or any installment of principal of or interest on (except as provided in Section 312 of the Indenture), any Debenture, or reduce the principal amount thereof or the rate of interest thereon (or the amount of any installment of interest thereon) or change the method of calculating such rate or reduce any premium payable upon the redemption thereof, or change the coin or currency (or other property), in which the Debentures or any premium or the interest thereon is payable, or impair the right to institute suit for the enforcement of any such payment on or after the Stated Maturity of any Debenture or (ii) reduce the percentage in principal amount of the Outstanding Debentures of any series or any Tranche thereof, the consent of the Holders of which is required for any such modification of the Indenture. The Indenture also contains provisions permitting Holders of specified percentages in principal amount of the Debentures at the time Outstanding, on behalf of the Holders of all Debentures, to waive compliance by the Company with

certain provisions of the Indenture and certain past defaults under the Indenture and their consequences. Any such consent or waiver by the Holder of this Debenture shall be conclusive and binding upon such Holder and upon all future Holders of this Debenture and of any Debenture issued upon the registration of transfer hereof or in exchange herefor or in lieu hereof, whether or not notation of such consent or waiver is made upon this Debenture.

No reference herein to the Indenture and no provision of this Debenture or of the Indenture shall alter or impair the obligation of the Company, which is absolute and unconditional, to pay the principal of and interest on this Debenture at the times, place and rate, and in the coin or currency, herein prescribed.

As provided in the Indenture and subject to certain limitations, including, if this Debenture is a global Debenture, the limitations set forth on the first page hereof, therein set forth, the transfer of this Debenture is registrable in the Security Register, upon surrender of this Debenture for registration of transfer at the office or agency of the Company in The City of New York maintained for such purpose, duly endorsed by, or accompanied by a written instrument of transfer in form satisfactory to the Company and the Security Registrar duly executed by, the Holder hereof or her attorney duly authorized in writing, and thereupon one or more new Debentures, of authorized denominations and for the same aggregate principal amount, will be issued to the designated transferee or transferees. No service charge shall be made for any such registration of transfer or exchange, but the Company may require payment of a sum sufficient to cover any tax or other governmental charge payable in connection therewith.

Prior to due presentment of this Debenture for registration of transfer, the Company, the Trustee and any agent of the Trustee may treat the Person in whose name this Debenture is registered as the owner hereof for all purposes, whether or not this Debenture be overdue, and neither the Company, the Trustee nor any such agent shall be affected by notice to the contrary.

The Debentures are issuable only in registered form without coupons in minimum denominations of $2,000 and integral multiples of $1,000 in excess thereof.

All terms used in this Debenture which are defined in the Indenture, as supplemented by the Officer’s Certificate, shall have the meanings set forth therein.