NIST Hydrocarbon C4H8 tables

C₄H₈ - 1-Butene

Molecular constants for the ground vibrational state of *cis*-1-butene and *skew*-1-butene
Parameter	cis-1-butene	skew-1-butene	Ref.
Rotational Constants
A″ [MHz]	15 302.559(25)	22557.431(33)	^a
B″ [MHz]	5574.9560(64)	4156.123(13)
C″ [MHz]	4303.1269(75)	4056.202(13)
τ₁ [kHz]	^b	0.2425(66)
τ₂ [kHz]	-4.3111(4)	28.50(221)
τ₃ [kHz]	0.37(3)	6.86(150)
τ_aaaa [kHz]	-0.103(21)	^b
τ_bbbb [kHz]	-21.528(804)	-8.422(2053)
τ_cccc [kHz]	-5.093(1009)	-15.033(2020)
Electric Dipole Moment
µ_a [C · m] µ_a [D]	1.228(13) x 10^-30 0.368(4)	1.151(23) x 10^-30 0.345(7)	68043
µ_b [C · m] µ_b [D]	0.791(20) x 10^-30 0.237(6)	0.270(37) x 10^-30 0.081(11)
µ_c [C · m] µ_c [D]		0.197(53) x 10^-30 0.059(16)

^a J. Phys. Chem. Ref. Data 18(3), 1245-1524 (1989).

^b Not determinable. Comments: An error in reference [68043] has been corrected. The 1₁₁-0₀₀ transition frequency for skew-1-butene should be 26 713.84 rather than 26 613.84.

Molecular constants for excited vibrational states of 1-butene
Parameter	cis-1-butene	skew-1-butene	Ref.
CC Torsion υ=1
A [MHz]	15338.60	22545.89	68043
B [MHz]	5539.25	4166.65
C [MHz]	4301.14	4068.25
CC Torsion υ=2
A [MHz]	15392.70	22542.82 ^a 22543.99 ^a
B [MHz]	5516.67	4177.15
C [MHz]	4294.62	4078.45
Methyl Torsion υ=1
A [MHz]	15274.57	22571.19
B [MHz]	5547.22	4150.52
C [MHz]	4290.53	4052.51
Methyl Torsion υ=2
A [MHz]	15274.57
B [MHz]	5519.95
C [MHz]	4278.05
Skeletal Bend υ=1
B [MHz]		4148.85
C [MHz]		4043.08

^a The two values refer to the doublet components for the J(1,J-1) and J(0,J).

Rotational constants for deuterated and ¹³ isotopic forms of 1-butene
Species ^a	Parameter	cis-1-butene	skew-1-butene	Ref.
1-d	A [MHz]	15 154.73	22 159.8	68043
	B [MHz]	5197.01	3924.04
	C [MHz]	4063.89	3823.00
2-d	A [MHz]	14 279.29	21 083.7
	B [MHz]	5518.02	4006.04
	C [MHz]	4185.50	3924.16
3-d	A [MHz]	14 381.80	20477.
	B [MHz]	5456.94	4108.80
	C [MHz]	4159.06	4002.65
4-d	A [MHz]	14 261.64	20342.4
	B [MHz]	5474.89	4113.03
	C [MHz]	4207.41	3981.11
5-d	A [MHz]		20592.9
	B [MHz]		4143.13
	C [MHz]		3993.69
6-d	A [MHz]	15 233.15
	B [MHz]	5209.19	3925.09
	C [MHz]	4077.42	3837.82
7-d	A [MHz]	14367.82
	B [MHz]	5441.16	4023.63
	C [MHz]	4197.86	3902.19
8-d	B [MHz]		4047.80
8-d	C [MHz]		3946.61
1,1-d₂	A [MHz]	14 187.125(11)	20 858.(200)	81038
	B [MHz]	5148.606(4)	3795.009(34)	80033
	C [MHz]	3962.463(4)	3710.571(34)	80033
1,3-d₂	A [MHz]	14197.37	20173.	68043
	B [MHz]	5105.83	3880.38
	C [MHz]	3937.88	3780.03
2,3-d₂	B [MHz]		3980.54
2,3-d₂	C [MHz]		3857.63
4,5-d₂	B [MHz]		4081.14
4,5-d₂	C [MHz]		3939.25
4,6-d₂	B [MHz]		3886.88
4,6-d₂	C [MHz]		3774.58
4,7-d₂	B [MHz]		3974.43
4,7-d₂	C [MHz]		3844.13
4,8-d₂	B [MHz]		4024.61
4,8-d₂	C [MHz]		3861.02
5,6-d₂	B [MHz]		3915.52
5,6-d₂	C [MHz]		3782.18
5,7-d₂	B [MHz]		4016.84
5,7-d₂	C [MHz]		3839.49
5,8-d₂	B [MHz]		4021.58
5,8-d₂	C [MHz]		3901.38
d₈	A [MHz]	10 597.801(8)		81038
	B [MHz]	4412.849(6)	3313.17	79033
	C [MHz]	3374.997(6)	3221.16	79033
1-¹³C	A [MHz]	15 148.537(16)		81038
	B [MHz]	5442.077(3)	4044.66	79033
	C [MHz]	4211.638(3)	3952.64	79033
4-¹³C	B [MHz]		4053.72	79033
	C [MHz]		3956.64	79033

^a See references [68043] and 79033] for hydrogen atom numbering.

Centrifugal distortion constants for isotopic forms of 1-butene
Parameter	cis-1,1-d₂	cis-1-¹³C	cis-1-d₈	Ref.	skew-1,1-d₂	Ref.
Δ_J [kHz]	2.959(56)	3.37(6)	2.01(12)	81038	3.13(24)	80033
Δ_JK [kHz]	-7.94(32)	-9.90(27)	-4.16(15)		-53.89(72)	80033
Δ_K [kHz]	24.8(12)	31.7(34)	11.6(10)
δ_J [kHz]	0.888(25)	0.991(14)	0.590(10)		-0.82(40)	80033
δ_K [kHz]	3.67(7)	4.15(36)	1.06(22)

C₄H₈ - *cis*-2-Butene

Molecular constants for *cis*-2-butene in the ground state
Parameter	CH₃CHCHCH₃	Ref.	Parameter	CH₃CHCHCH₃		Ref.
Parameter	A₁A₁ State	Ref.	Parameter	Rigid Rotor	A₁A₁ State	Ref.
Rotational Constants
A [MHz]	16086.12	70067	A [MHz]	16059.61	16085.76	68049
B [MHz]	5144.33		B [MHz]	5139.15	5144.61
C [MHz]	4087.93		C [MHz]	4088.16	4088.16
Internal Rotational Constants
I_α (u Å²)	3.130	70067	I_α (u Å²)	3.194 ^a		68049
λ_a	0.5850(12)		λ_a	35.0° ^a
λ_b	0.8111(9)
r	0.94504		α	0.058 199 ^b
q	0.0131		β	0.026 598 ^b
s	20.39(11)		s	20.332
F [GHz]	170.937		F [GHz]	167.54
V₃ (cm^-1)	261.7(14)		V₃ (cm^-1)	255.8
Electric Dipole Moment
µ_b [C · m] µ_b [D]	0.844(17) x 10^-30 0.253(5)	70067	µ_b [C · m] µ_b [D]	0.857(33) x 10^-30 0.257(10)		68049

^a Assumed.

^b The values are defined as α = (I_α/I_a) sinθ, β = (I_α/I_b) cosθ.

Comments: The 7₁₆ - 7₀₇ transition reported at 31 829.11 MHz deviates by about 3 MHz in the analysis and was not fit.

Molecular constants for *sym*-CH₂DCHCHCH₃, *asy*-CH₂DCHCHCH₃, and CH₃CDCDCH₃
Parameter	sym-CH₂DCHCHCH₃ Value	asy-CH₂DCHCHCH₃ Value	CH₃CDCDCH₃ Value	Ref.
Rotational Constants
A-C (A₁) [MHz]	11 040.37	11 681.12	10 033.99	70067
B-C (A₁) [MHz]	1101.06	938.69	1155.42
A-C (A₂) [MHz]		11 672.24
B-C (A₂) [MHz]		937.77
Internal Rotational Constants ^a
λ_a	0.5538(16)	0.5684(28)	0.5883(54)
λ_b	0.8259(12)	0.8228(20) ^b	0.8086(39)
I_α (u Å²)	3.130	3.130	3.130
r	0.94904	0.94823	0.95002
F [GHz]	170.184	170.329	170.026
s	20.42(2)	20.66(4)	20.96(7)
V₃ (cm^-1)	260.9(3)	264.2(5)	267.6(9)

^a Values with no uncertainties are calculated from other constants.

^b Value for λ_c = 0.0034 was included.

Molecular constants for CH₃CDCHCH₃
Parameter	Value		Ref.
Rotational Constants
A-C (A₁A₁) [MHz]	10 942.28		70067
B-C (A₁A₁) [MHz]	1107.63
Internal Rotational Constants ^a
	A₁ State	A₂ State
λ_a	-0.5700(164)	0.6118(124)
λ_b	0.8216(114)	0.7910(96)
I_α (u Å²)	3.130	3.130
r	0.948 83	0.948 83
q	0.011 78	0.011 78
F [GHz]	170.248	170.248
s	20.68(11)	20.61(11)
x	-0.012 45
V₃ (cm^-1)	264.4(14)	264.4(14)

^a Values without uncertainties are calculated from other constants.

Molecular constants for d₈ and d₆ *cis*-2-butene
Parameter	CD₃CDCDCD₃	CD₃CHCHCD₃	Ref.
Rotational Constants
A [MHz]	11 136.1(3)	12 684.2(2)	79039
B [MHz]	3997.05(14)	4008.11(4)
C [MHz]	3170.96(11)	3346.45(4)
Internal Rotational Constants
I_α (u Å²)	5.83(20)	5.98(20)
θ	54.08(12)	54.27(1)
s	40.34(10)	39.31(8)
V₃ (cm^-1)	284.(11)	272.(11)

C₄H₈ - Isobutylene

Molecular constants for isobutylene (2-methl propene) in the ground and torionally excited states
	(CH₃)₂C=CH₂
Parameter	Ground State	υ_t = 1₁ State	υ_t = 1₂ State	Ref.
Rotational Constants ^a
A [MHz]	9133.31(3)	9132.01(3)	9140.61(3)	75058
B [MHz]	8381.80(3)	8369.09(3)	8353.22(3)
C [MHz]	4615.97(2)	4613.46(2)	4613.41(2)
Δ_JK [kHz]	-16.70(7)
Δ_J [kHz]	7.88(46)
δ_J [kHz]	-65.3(30)
δ_K [kHz]	-19.385(48)
Internal Rotational Constants
I_α (u Å²)	3.18(1)	3.18 ^b
θ	58.21(6)°	58.21 ^b
V₃ (cm^-1)	759.8(32)	767.9(35)
V′₁₂ (cm^-1)		-74.(11)
Δ₀ [MHz]	-9.659(58)
ρ	0.056 20(20)
β [rad]	0.5172(12)
Electric Dipole Moment
µ_b [C · m] µ_b [D]	1.678(30) x 10^-30 0.503(9)			61014

^a Representation III^r was used.

^b Values fixed.

Rotational analysis of isobutylene AA state
Parameter	AA State	Ref.
A″ [MHz]	9133.392(35)	^a
B″ [MHz]	8381.846(35)
C″ [MHz]	4615.966(35)
τ₁ [kHz]	-0.021(25)
τ₂ [kHz]	-0.0054(84)
τ₃ [kHz]	0.60(25) ^b
τ_aaaa [kHz]	-0.028(8)
τ_bbbb [kHz]	-0.029(8)
τ_cccc [kHz]	0.0041(85)

^a J. Phys. Chem. Ref. Data 18(3), 1245-1524 (1989).

^b The value of τ₃ is fixed by setting R₆ = 0.

Rotational constants for deuterated and ¹³C isotopic species of isobutylene
Species	A [MHz]	B [MHz]	C [MHz]	Ref.
sym-CH₂DCH₃CCH₂	9132.59	7788.98	4431.05	61014
asy-CH₂DCH₃CCH₂	8819.46	7981.08	4469.59	61014
(CH₃)₂CCHD	8693.49	8114.67	4422.67	63027
(CH₃)₂C¹³CH₂	8810.08	8381.73	4531.84
CH₃¹³CH₃CCH₂	9074.31	8149.00	4529.72

C₄H₈ - Methylcyclopropane

Molecular constants for methylcyclopropane
Parameter		Ref.
Rotational Constants
A″ [MHz]	15 503.225(33)	^a
B″ [MHz]	6363.4072(78)
C″ [MHz]	5586.4839(69)
τ₁ [kHz]	-0.0077(53)
τ₂ [kHz]	-0.0017(15)
τ₃ ^b [kHz]	0.147(58)
τ_aaaa [kHz]	-0.112(41)
τ_bbbb [kHz]	-0.0028(6)
Internal Rotation Barrier
V₃ (cm^-1)	1001.(18)	68048
Dipole Moment
µ_a [C · m] µ_a [D]	0.324(3) x 10^-30 0.097(1)	68048
µ_c [C · m] µ_c [D]	0.334(17) x 10^-30 0.100(5)	68048

^a J. Phys. Chem. Ref. Data 18(3), 1245-1524 (1989).

^b The value of τ₃ is fixed by setting R₆ = 0.

C₄H₈ - Cyclobutane-d₁

Molecular constants for cyclobutane-d₁
Parameter	Equatorian	Axial	Ref.
A [MHz]	10 617.908(17)	10 377.613(18)	87024
B [MHz]	9817.535(17)	9975.708(18)
C [MHz]	6050.794(17)	6193.449(18)
Δ_J [kHz]	4.3(22)	5.3(20)
Δ_JK [kHz]	-3.18(89)	-4.4(12)
Δ_K [kHz]	6.04(66)	6.25(83)
δ_J [kHz]	0.79(13)	0.95(19)
δ_K [kHz]	1.31(37)	0.65(45)
H_KJ [Hz]	-0.0079(6)	-0.014(7)
Electric Dipole Moment
µ_a [C · m] µ_a [D]	0.0143(47) x 10^-30 0.0043(14)		87024
µ_c [C · m] µ_c [D]		0.0143(47) x 10^-30 0.0043(14)	87024

C₄H₈ - 1-Butene

Molecular constants for the ground vibrational state of cis-1-butene and skew-1-butene

Molecular constants for excited vibrational states of 1-butene

Rotational constants for deuterated and ¹³ isotopic forms of 1-butene

Centrifugal distortion constants for isotopic forms of 1-butene

C₄H₈ - cis-2-Butene

Molecular constants for cis-2-butene in the ground state

Molecular constants for sym-CH₂DCHCHCH₃, asy-CH₂DCHCHCH₃, and CH₃CDCDCH₃

Molecular constants for CH₃CDCHCH₃

Molecular constants for d₈ and d₆ cis-2-butene

C₄H₈ - Isobutylene

Molecular constants for isobutylene (2-methl propene) in the ground and torionally excited states

Rotational analysis of isobutylene AA state

Rotational constants for deuterated and ¹³C isotopic species of isobutylene

C₄H₈ - Methylcyclopropane

Molecular constants for methylcyclopropane

C₄H₈ - Cyclobutane-d₁

Molecular constants for cyclobutane-d₁

C4H8 - 1-Butene

Molecular constants for the ground vibrational state of cis-1-butene and skew-1-butene

Molecular constants for excited vibrational states of 1-butene

Rotational constants for deuterated and 13 isotopic forms of 1-butene

Centrifugal distortion constants for isotopic forms of 1-butene

C4H8 - cis-2-Butene

Molecular constants for cis-2-butene in the ground state

Molecular constants for sym-CH2DCHCHCH3, asy-CH2DCHCHCH3, and CH3CDCDCH3

Molecular constants for CH3CDCHCH3

Molecular constants for d8 and d6 cis-2-butene

C4H8 - Isobutylene