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          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" xlink:label="loc_cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" xml:lang="en-US">Special Risks Related to Certain Municipal Obligations [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" xlink:to="lab_cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_StructuredProductsRiskMember" xlink:label="loc_cik0000818851_StructuredProductsRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_StructuredProductsRiskMember" xml:lang="en-US">Structured Products Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_StructuredProductsRiskMember" xlink:to="lab_cik0000818851_StructuredProductsRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_SwapTransactionsRiskMember" xlink:label="loc_cik0000818851_SwapTransactionsRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_SwapTransactionsRiskMember" xml:lang="en-US">Swap Transactions Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_SwapTransactionsRiskMember" xlink:to="lab_cik0000818851_SwapTransactionsRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_TaxRiskMember" xlink:label="loc_cik0000818851_TaxRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_TaxRiskMember" xml:lang="en-US">Tax Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_TaxRiskMember" xlink:to="lab_cik0000818851_TaxRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_TaxabilityRiskMember" xlink:label="loc_cik0000818851_TaxabilityRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_TaxabilityRiskMember" xml:lang="en-US">Taxability Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_TaxabilityRiskMember" xlink:to="lab_cik0000818851_TaxabilityRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_TobaccoSettlementBondRiskMember" xlink:label="loc_cik0000818851_TobaccoSettlementBondRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_TobaccoSettlementBondRiskMember" xml:lang="en-US">Tobacco Settlement Bond Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_TobaccoSettlementBondRiskMember" xlink:to="lab_cik0000818851_TobaccoSettlementBondRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_UnratedSecuritiesRiskMember" xlink:label="loc_cik0000818851_UnratedSecuritiesRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_UnratedSecuritiesRiskMember" xml:lang="en-US">Unrated Securities Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_UnratedSecuritiesRiskMember" xlink:to="lab_cik0000818851_UnratedSecuritiesRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_ValuationRiskMember" xlink:label="loc_cik0000818851_ValuationRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_ValuationRiskMember" xml:lang="en-US">Valuation Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_ValuationRiskMember" xlink:to="lab_cik0000818851_ValuationRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" xlink:label="loc_cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" xml:lang="en-US">When-Issued and Delayed-Delivery Transactions Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" xlink:to="lab_cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" xlink:label="loc_cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" xml:lang="en-US">Zero Coupon Bonds Risk or Pay-In-Kind Securities Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" xlink:to="lab_cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_AntiTakeoverProvisionsRiskMember" xlink:label="loc_cik0000818851_AntiTakeoverProvisionsRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_AntiTakeoverProvisionsRiskMember" xml:lang="en-US">Anti-Takeover Provisions Risk</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_AntiTakeoverProvisionsRiskMember" xlink:to="lab_cik0000818851_AntiTakeoverProvisionsRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_CounterpartyRisk.Member" xlink:label="loc_cik0000818851_CounterpartyRisk.Member" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_CounterpartyRisk.Member" xml:lang="en-US">Counterparty Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_CounterpartyRisk.Member" xlink:to="lab_cik0000818851_CounterpartyRisk.Member" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_CybersecurityRiskMember" xlink:label="loc_cik0000818851_CybersecurityRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_CybersecurityRiskMember" xml:lang="en-US">Cybersecurity Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_CybersecurityRiskMember" xlink:to="lab_cik0000818851_CybersecurityRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_EconomicAndPoliticalEventsRiskMember" xlink:label="loc_cik0000818851_EconomicAndPoliticalEventsRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_EconomicAndPoliticalEventsRiskMember" xml:lang="en-US">Economic and Political Events Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_EconomicAndPoliticalEventsRiskMember" xlink:to="lab_cik0000818851_EconomicAndPoliticalEventsRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_FundTaxRiskMember" xlink:label="loc_cik0000818851_FundTaxRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_FundTaxRiskMember" xml:lang="en-US">Fund Tax Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_FundTaxRiskMember" xlink:to="lab_cik0000818851_FundTaxRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_GlobalEconomicRiskMember" xlink:label="loc_cik0000818851_GlobalEconomicRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_GlobalEconomicRiskMember" xml:lang="en-US">Global Economic Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_GlobalEconomicRiskMember" xlink:to="lab_cik0000818851_GlobalEconomicRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_InvestmentAndMarketRiskMember" xlink:label="loc_cik0000818851_InvestmentAndMarketRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_InvestmentAndMarketRiskMember" xml:lang="en-US">Investment and Market Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_InvestmentAndMarketRiskMember" xlink:to="lab_cik0000818851_InvestmentAndMarketRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_LegislationAndRegulatoryRiskMember" xlink:label="loc_cik0000818851_LegislationAndRegulatoryRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_LegislationAndRegulatoryRiskMember" xml:lang="en-US">Legislation and Regulatory Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_LegislationAndRegulatoryRiskMember" xlink:to="lab_cik0000818851_LegislationAndRegulatoryRiskMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_MarketDiscountFromNetAssetValueMember" xlink:label="loc_cik0000818851_MarketDiscountFromNetAssetValueMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_MarketDiscountFromNetAssetValueMember" xml:lang="en-US">Market Discount from Net Asset Value [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_MarketDiscountFromNetAssetValueMember" xlink:to="lab_cik0000818851_MarketDiscountFromNetAssetValueMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_RecentMarketConditionsMember" xlink:label="loc_cik0000818851_RecentMarketConditionsMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_RecentMarketConditionsMember" xml:lang="en-US">Recent Market Conditions [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_RecentMarketConditionsMember" xlink:to="lab_cik0000818851_RecentMarketConditionsMember" />
          <link:loc xlink:type="locator" xlink:href="cik0000818851-20260831.xsd#cik0000818851_ReverseRepurchaseAgreementRiskMember" xlink:label="loc_cik0000818851_ReverseRepurchaseAgreementRiskMember" />
          <link:label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="lab_cik0000818851_ReverseRepurchaseAgreementRiskMember" xml:lang="en-US">Reverse Repurchase Agreement Risk [Member]</link:label>
          <link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_cik0000818851_ReverseRepurchaseAgreementRiskMember" xlink:to="lab_cik0000818851_ReverseRepurchaseAgreementRiskMember" />
        </link:labelLink>
      </link:linkbase>
    </appinfo>
  </annotation>
  <import namespace="http://xbrl.sec.gov/cef/2026" schemaLocation="https://xbrl.sec.gov/cef/2026/cef-2026.xsd" />
  <import namespace="http://xbrl.sec.gov/cef-pre/2026" schemaLocation="https://xbrl.sec.gov/cef/2026/cef-2026_pre.xsd" />
  <import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd" />
  <import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd" />
  <import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd" />
  <import namespace="http://xbrl.sec.gov/dei/2026" schemaLocation="https://xbrl.sec.gov/dei/2026/dei-2026.xsd" />
  <import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" />
  <import namespace="http://www.xbrl.org/dtr/type/2020-01-21" schemaLocation="https://www.xbrl.org/dtr/type/2020-01-21/types.xsd" />
  <element name="CommonSharesMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CommonSharesMember" substitutionGroup="xbrli:item" />
  <element name="AlternativeMinimumTaxRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_AlternativeMinimumTaxRiskMember" substitutionGroup="xbrli:item" />
  <element name="BelowInvestmentGradeRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_BelowInvestmentGradeRiskMember" substitutionGroup="xbrli:item" />
  <element name="CallRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CallRiskMember" substitutionGroup="xbrli:item" />
  <element name="CreditRisksMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CreditRisksMember" substitutionGroup="xbrli:item" />
  <element name="CreditSpreadRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CreditSpreadRiskMember" substitutionGroup="xbrli:item" />
  <element name="DefaultedOrDistressedSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_DefaultedOrDistressedSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="DeflationRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_DeflationRiskMember" substitutionGroup="xbrli:item" />
  <element name="DerivativesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_DerivativesRiskMember" substitutionGroup="xbrli:item" />
  <element name="DurationRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_DurationRiskMember" substitutionGroup="xbrli:item" />
  <element name="EconomicSectorRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_EconomicSectorRiskMember" substitutionGroup="xbrli:item" />
  <element name="FloatingAndVariableRateSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_FloatingAndVariableRateSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="FinancialFuturesAndOptionsTransactionsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_FinancialFuturesAndOptionsTransactionsRiskMember" substitutionGroup="xbrli:item" />
  <element name="HedgingRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_HedgingRiskMember" substitutionGroup="xbrli:item" />
  <element name="IncomeRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_IncomeRiskMember" substitutionGroup="xbrli:item" />
  <element name="InflationRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_InflationRiskMember" substitutionGroup="xbrli:item" />
  <element name="InsuranceRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_InsuranceRiskMember" substitutionGroup="xbrli:item" />
  <element name="InverseFloatingRateSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_InverseFloatingRateSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="MunicipalSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_MunicipalSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="MunicipalSecuritiesMarketLiquidityRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_MunicipalSecuritiesMarketLiquidityRiskMember" substitutionGroup="xbrli:item" />
  <element name="MunicipalSecuritiesMarketRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_MunicipalSecuritiesMarketRiskMember" substitutionGroup="xbrli:item" />
  <element name="OtherInvestmentCompaniesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_OtherInvestmentCompaniesRiskMember" substitutionGroup="xbrli:item" />
  <element name="PuertoRicoMunicipalSecuritiesMarketRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_PuertoRicoMunicipalSecuritiesMarketRiskMember" substitutionGroup="xbrli:item" />
  <element name="ReinvestmentRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_ReinvestmentRiskMember" substitutionGroup="xbrli:item" />
  <element name="RestrictedAndIlliquidInvestmentsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_RestrictedAndIlliquidInvestmentsRiskMember" substitutionGroup="xbrli:item" />
  <element name="SpecialConsiderationsRelatedToSingleStateConcentrationRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_SpecialConsiderationsRelatedToSingleStateConcentrationRiskMember" substitutionGroup="xbrli:item" />
  <element name="SpecialRisksRelatedToCertainMunicipalObligationsMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_SpecialRisksRelatedToCertainMunicipalObligationsMember" substitutionGroup="xbrli:item" />
  <element name="StructuredProductsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_StructuredProductsRiskMember" substitutionGroup="xbrli:item" />
  <element name="SwapTransactionsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_SwapTransactionsRiskMember" substitutionGroup="xbrli:item" />
  <element name="TaxRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_TaxRiskMember" substitutionGroup="xbrli:item" />
  <element name="TaxabilityRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_TaxabilityRiskMember" substitutionGroup="xbrli:item" />
  <element name="TobaccoSettlementBondRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_TobaccoSettlementBondRiskMember" substitutionGroup="xbrli:item" />
  <element name="UnratedSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_UnratedSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="ValuationRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_ValuationRiskMember" substitutionGroup="xbrli:item" />
  <element name="WhenIssuedAndDelayedDeliveryTransactionsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_WhenIssuedAndDelayedDeliveryTransactionsRiskMember" substitutionGroup="xbrli:item" />
  <element name="ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_ZeroCouponBondsRiskOrPayInKindSecuritiesRiskMember" substitutionGroup="xbrli:item" />
  <element name="AntiTakeoverProvisionsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_AntiTakeoverProvisionsRiskMember" substitutionGroup="xbrli:item" />
  <element name="CounterpartyRisk.Member" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CounterpartyRisk.Member" substitutionGroup="xbrli:item" />
  <element name="CybersecurityRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_CybersecurityRiskMember" substitutionGroup="xbrli:item" />
  <element name="EconomicAndPoliticalEventsRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_EconomicAndPoliticalEventsRiskMember" substitutionGroup="xbrli:item" />
  <element name="FundTaxRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_FundTaxRiskMember" substitutionGroup="xbrli:item" />
  <element name="GlobalEconomicRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_GlobalEconomicRiskMember" substitutionGroup="xbrli:item" />
  <element name="InvestmentAndMarketRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_InvestmentAndMarketRiskMember" substitutionGroup="xbrli:item" />
  <element name="LegislationAndRegulatoryRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_LegislationAndRegulatoryRiskMember" substitutionGroup="xbrli:item" />
  <element name="MarketDiscountFromNetAssetValueMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_MarketDiscountFromNetAssetValueMember" substitutionGroup="xbrli:item" />
  <element name="RecentMarketConditionsMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_RecentMarketConditionsMember" substitutionGroup="xbrli:item" />
  <element name="ReverseRepurchaseAgreementRiskMember" type="dtr-types:domainItemType" abstract="true" xbrli:periodType="duration" nillable="true" id="cik0000818851_ReverseRepurchaseAgreementRiskMember" substitutionGroup="xbrli:item" />
</schema>
