NIST Hydrocarbon C4H6 tables

C₄H₆ - 2-Butyne-1,1,1-d₃

Molecular constants for 2-butyne-1,1,1-d₃ (dimethyl acetylene)
Parameter	Value ^a	Ref.
B [MHz]	2982.4980(11)	84027
D_J [kHz]	0.2570(9)
D_JK [kHz]	9.776(12)
G [kHz]	-93.90(11)
L [kHz]	25.97(6)
C [kHz]	-38.2(1)
s²L [kHz]	2.65(15)
s ^b	0.319(9)
V₃ ^b (cm^-1)	5.62(16)
F ^b [kHz]	-123.2(75)

^a The uncertainties are 2.5 times standard deviations. See [84027] for definition of parameters.

^b Derived from other constants.

C₄H₆ - 1-Butyne

Molecular constants for 1-butyne (C₄H₆) in the ground and lowest torsional and bending states
Parameter	Ground State	ν₂₄ = 1 Methyl torsion	ν₁₅ = 1 C≡C-C	Ref.
A″ [MHz]	27 147.8126(50)	28 014.44(97)	26 407.94(25)	^a
B″ [MHz]	4546.479 32(83)	4544.7101(82)	4559.084(8)
C″ [MHz]	4086.875 10(80)	4086.3148(95)	4092.689(4)
τ₁ [kHz]	0.150 285(16)	0.2328(30)	0.0786(13)
τ₂ [kHz]	0.011 8211(46)	0.023 17(52)	-0.69(170) x 10^-4
τ₃ ^b [kHz]	1.019(1)	1.31(12)	0.077(26)
τ_aaaa [kHz]	-2.147 587(584)	-2.75(354)	3.71(78)
τ_bbbb [kHz]	-0.016 0141(43)	-0.015 469(83)	-0.015 969(65)
τ_cccc [kHz]	-0.005 9185(41)	-0.004 26(38)	-0.005 428(16)
H_J [Hz]	0.009 33(36)
H_JK [Hz]	-0.3410(280)		-4.84(41)
H_KJ [Hz]	-0.6504(933)
H_K [Hz]	33.55(130)
h_J [Hz]	0.006 81(22)
h_JK [Hz]	0.1754(238)
h_K [Hz]	-15.68(196)
Internal Rotation Constants
ω₁(s)	-0.1469(12) x 10^-5			85014, 83039
θ(a,i)	47.55(19)°	48.454(13)°
I_α (u Å²)	3.180(12)	3.1635 ^c
s	82.81(8)	86.57(26)
F [GHz]	175.30(66)	176.162
V₃ (cm^-1)	1089.9(53)	1144.8(4)
Electric Dipole Moment
µ_a [C · m] µ_a [D]	2.545(10) x 10^-30 0.763(3)			83038
µ_b [C · m] µ_b [D]	0.567(13) x 10^-30 0.170(4)			83038

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

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

^c Assumed value.

Molecular constants for the vibrationally excited states ν₁₅ = 2, ν₁₅ = 3, and ν₁₄ = 1 of 1-butyne

Vibrational State

A [MHz]

B [MHz]

C [MHz]

D_JK [kHz]

Ref.

ν₁₅ = 2

25 728.(39)

4571.424(23)

4098.195(23)

-8.8(21)

83038

ν₁₅ = 3

25 000.(32)

4583.534(26)

4103.500(29)

21.2(25)

ν₁₄ = 1

26 991.(38)

4547.096(23)

4091.436(23)

-45.6(22)

Comments: The following transitions were not included in the fit:

Transition for the ν₂₄ = 1 state:	Frequency [MHz]	Δν(obs-cal) [MHz]
18_2,17 - 17_2,16	154 299.32	-0.58
18_3,15 - 17_3,14	156 595.53	0.26
18_2,17 - 17_2,16	157 387.87	0.14
Transition for the ν₁₅ = 1 state:
4₁₃ - 4₀₄	24 504.22	-2.02
27_3,24 - 27_3,25	30 421.88	-4.35
17_6,12 - 16_6,11	14 7247.37	-0.82
17_5,13 - 16_5,12	147 316.53	-0.40
18_5,14 - 17_5,13	156 006.17	-0.56
25_1,24 - 24_1,23	215 354.31	-0.45
25_3,23 - 24_3,22	216 453.67	+0.93
27_1,26 - 26_1,25	231 539.29	-1.02

C₄H₆ - 1,2-Butadiene

Molecular constants for 1,2-butadiene (methyl allene)
Parameter	Value	Ref.
Rotational Constants
A [MHz]	34 023.(46)	^a
B [MHz]	4201.278(14)
C [MHz]	3928.099(15)
Δ_J [kHz]	1.78(16)
Δ_JK [kHz]	-56.82(63)
δ_J [kHz]	0.32(25)
Internal Rotational Constants ^b
I_α (u Å²)	3.103
θ	38.16°
V₃ (cm^-1)	556.94(87)
Δ₀ [MHz]	-151.9
β	0.096 73
ρ	0.165 03
Dipole Moment
µ_c [C · m] µ_c [D]	1.314(7) x 10^-30 0.394(2)	57016
µ_b [C · m] µ_b [D]	0.233(3) x 10^-30 0.070(1)	57016

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

^b Only the rotational constants and V₃ were fit.

C₄H₆ - Bicyclo[1.1.0.]butane

Molecular constants for bicyclo[1.1.0.]butane
Species	A [MHz]	B [MHz]	C [MHz]	Ref.
Rotational Constants
	17 311.974(40)	9313.516(32)	8393.521(30)	^a
(1-¹³C)	16 934.17(14)	9298.37(18)	8316.53(14)	69057
(2-¹³C)	17 256.84(13)	9085.62(17)	8220.44(13)
(7,9-D₂)	16 221.47(13)	8164.35(17)	7670.79(13)
(5-D)	15 554.92(8)	9151.50(10)	8077.18(8)
Dipole Moment
µ_c [C · m] µ_c [D]	2.25(3) x 10^-30 0.67₅(1₀)			66041
Zeeman Constants
g_aa	0.0593(2) ^b µ_N			72061
g_bb	0.0025(2) ^b µ_N
g_cc	0.0412(2) ^b µ_N
2χ_aa - χ_bb - χ_cc	-5.9(3) x 10^-6 erg/G² · mol
-χ_aa + 2χ_bb - χ_cc	21.1(3) x 10^-6 erg/G² · mol

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

^b Sign not determined, but positive values are favored.

C₄H₆ - Cyclobutene

Molecular constants for cyclobutene and its ¹³C isotopic species
Parameter	Cyclobutene	1-¹³C-Cyclobutene	3-¹³C-Cyclobutene	Ref.
Rotational Constants
A″ [MHz]	12 892.8825(23)	12 784.7842(71)	12 742.881(16)	^a
B″ [MHz]	12 226.1058(22)	12 015.5953(71)	12 033.857(16)
C″ [MHz]	6816.2674(13)	6720.5173(65)	6714.547(14)
τ₁ [kHz]	-0.047 866(2693)	-0.051 34(301)	-0.047 76(664)
τ₂ [kHz]	-0.012 535(902)	-0.013 98(101)	-0.012 85(223)
τ₃ ^b [kHz]	1.80(3)	1.52(3)	1.58(8)
τ_aaaa [kHz]	-0.028 287(839)	-0.030 417(940)	-0.030 02(208)
τ_bbbb [kHz]	-0.026 388(860)	-0.028 334(961)	-0.027 62(212)
Electric Dipole Moment
µ_a [C · m] µ_a [D]	0.437(3) x 10^-30 0.131(1)			65029
Zeeman Constants
g_aa	-0.0516(7) µ_N			70063
g_bb	-0.0663(7) µ_N
g_cc	-0.0219(6) µ_N
2χ_aa - χ_bb - χ_cc	-0.9(5) x 10^-6 erg/G² · mol
-χ_aa + 2χ_bb - χ_cc	5.0(7) x 10^-6 erg/G² · mol
Q_aa	-0.3(6) x 10^-26 esu · cm²
Q_bb	1.6(7) x 10^-26 esu · cm²
Q_cc	-1.3(10) x 10^-26 esu · cm²

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

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

Molecular constants for monodeutero-species of cyclobutene
Parameter			Ref.
Rotational Constants
A″ [MHz]	12 658.7572(50)	12 419.2632(50)	^a
B″ [MHz]	11 220.9574(54)	11 431.6151(51)
C″ [MHz]	6432.0155(37)	6557.7960(33)
τ₁ [kHz]	-0.030 95(416)	-0.045 05(386)
τ₂ [kHz]	-0.008 33(138)	-0.012 90(129)
τ₃ ^b [kHz]	0.62(2)	0.92(3)
τ_aaaa [kHz]	-0.0297(11)	-0.0316(11)
τ_bbbb [kHz]	-0.0217(13)	-0.0268(12)

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

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

C₄H₆ - 1-Methyl cyclopropene

Molecular constants for 1-Methyl cyclopropene
Parameter	Ground State	Ref.	Torsional State	Ref.
Rotational Constants
A [MHz]	20 549.975(92)	^a	20 322.347	69066
B [MHz]	6357.084(28)		6342.620
C [MHz]	5176.431(17)		5172.440
Δ_J [kHz]	2.67(134)
Δ_JK [kHz]	9.98(314)
Δ_K [kHz]	77.0(72)
δ_J [kHz]	0.39(6)
δ_K [kHz]	6.9(50)
Internal Rotational Constants
I_α (u Å²)	3.124 ^b	^a	3.124 ^b	69066
θ	6.16° ^b
λ_a	0.994 23		0.9922(65)
λ_b	-0.107 30		-0.1262(52)
V₃ (cm^-1)	488.27(28)		483.3(7)
Dipole Moment
µ_a [C · m] µ_a [D]	2.728(27) x 10^-30 0.818(8)			69066
µ_b [C · m] µ_b [D]	0.63(7) x 10^-30 0.19(2)			69066

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

^b Assumed parameter.

Comments:In [69066] a quantum number error 6₁₆-6₁₆ has been corrected to 6₁₆-6₁₅ and the 8₂₇-8₂₆ transition deviates by 1 MHz and thus, was not fit.

C₄H₆ - Methylene Cyclopropane

Molecular constants for methylene cyclopropane
Parameter	Value	Ref.
A″ [MHz]	19 415.25(88)	^a
B″ [MHz]	6877.1615(65)
C″ [MHz]	5445.1776(80)
τ₁ [kHz]	-0.092 52(813)
τ₂ [kHz]	-0.017 84(239)
τ₃ ^b [kHz]	0.53(22)
τ_bbbb [kHz]	-0.0099(20)
τ_cccc [kHz]	-0.0052(24)
Dipole Moment
µ_a [C · m] µ_a [D]	1.341 x 10^-30 0.402	70062
Zeeman Constants
g_aa µ_N	-0.0672(7)	70063
g_bb µ_N	-0.0231(4)
g_cc µ_N	+0.0244(4)
2χ_aa - χ_bb - χ_cc	18.3(5) x 10^-6 erg/G² · mol
-χ_aa + 2χ_bb - χ_cc	14.9(6) x 10^-6 erg/G² · mol

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

^b Value of τ₃ fixed by setting R₆ = 0.

Rotational constants for the ¹³C isotopic species of methylene cyclopropane
Parameter				Ref.
A [MHz]	19 424.(10)	19 422.(10)	18 998.1(1)	70062
B [MHz]	6641.30(3)	6869.05(3)	6795.51(3)
C [MHz]	5296.18(3)	5440.07(3)	5360.78(3)

C4H6 - 2-Butyne-1,1,1-d3

Molecular constants for 2-butyne-1,1,1-d3 (dimethyl acetylene)

C4H6 - 1-Butyne

Molecular constants for 1-butyne (C4H6) in the ground and lowest torsional and bending states

Molecular constants for the vibrationally excited states ν15 = 2, ν15 = 3, and ν14 = 1 of 1-butyne

C4H6 - 1,2-Butadiene

Molecular constants for 1,2-butadiene (methyl allene)

C4H6 - Bicyclo[1.1.0.]butane

Molecular constants for bicyclo[1.1.0.]butane

C4H6 - Cyclobutene

Molecular constants for cyclobutene and its 13C isotopic species

Molecular constants for monodeutero-species of cyclobutene

C4H6 - 1-Methyl cyclopropene

Molecular constants for 1-Methyl cyclopropene

C4H6 - Methylene Cyclopropane

Molecular constants for methylene cyclopropane

Rotational constants for the 13C isotopic species of methylene cyclopropane

C₄H₆ - 2-Butyne-1,1,1-d₃

Molecular constants for 2-butyne-1,1,1-d₃ (dimethyl acetylene)

C₄H₆ - 1-Butyne

Molecular constants for 1-butyne (C₄H₆) in the ground and lowest torsional and bending states

Molecular constants for the vibrationally excited states ν₁₅ = 2, ν₁₅ = 3, and ν₁₄ = 1 of 1-butyne

C₄H₆ - 1,2-Butadiene

C₄H₆ - Bicyclo[1.1.0.]butane

C₄H₆ - Cyclobutene

Molecular constants for cyclobutene and its ¹³C isotopic species

C₄H₆ - 1-Methyl cyclopropene

C₄H₆ - Methylene Cyclopropane

Rotational constants for the ¹³C isotopic species of methylene cyclopropane