M. Douay et al- The Discovery of Two New Infrared Electronic Transitions of C2: B^1-Delta-g-A^1-Pi-u and B'^1-Sigma-g^+-A^1-Pi-u

8/2/2019 M. Douay et al- The Discovery of Two New Infrared Electronic Transitions of C2: B^1-Delta-g-A^1-Pi-u and B'^1-Sig

1/11

JOURNAL OF MOLECULAR SPECTROSCOPY 131,26 1-271 (1988)

The Discovery of Two New Infrared Electronic Transitions of C2:B A,-AllI, and B I$-A&

M. DOUAY, 'R. NIETMANN, AND P. F. BERNATH~Departm ent of Chemistry, University of Arizona, Tucson, Arizona 85 721

Two new infrared electronic transitions of C2, B AK-A II. and B El-A II., were observedby Fourier transform emission spectroscopy of hydrocarbon discharges. A set of spectroscopicconstants were derived for each vibrational level and then reduced to equilibrium constants,includingT, (cm-) u, (cm-) re (A)

BA, 12 082.3360(40) 1407.4653(13) 1.38548B Z+g 15 409.1390(39) 1424.1189 1.37735

RKR curves and Franck-Condon factors were calculated from the equilibrium constants.0 1988 Academic Press, Inc.

I. INTRODUCTIONDuring the course of our spectroscopic observation of the d1 F-b II transition of

Sic (I), A. D. McLean pointed out that the corresponding CZ transition( B Zi-A II,) had not been reported. This was quite surprising because the C2 mol-ecule occurs in such a wide variety of sources and has been studied for many years(see the preceding paper (2) for references). Examination of two previously recordedspectra disclosed the B Xi-AII, and B A,-A II, transitions, in addition tothe well-known Phillips system, A &,-X1 Z.g, and Ballik-Ramsay system,b3 X,-a3 II,. Our reanalysis of the Phillips System is reported in the precedingpaper (2).

The B A8 and B Zz states of C2 are predicted to be low-lying bound states by abinitio calculation (3-6). These two states do not connect with the ground X 2: statevia one-photon electric dipole selection rules. The infrared electronic transitionsB A,-A II, and B Zi-A II,, however, are quite strong (Figs. l-4). The maindifficulty is that the Ballik-Ramsay and Phillips systems (as well as the usual collectionof impurities such as CO, CN, CH, and ArH) make the infrared emission spectra ofhydrocarbon discharges quite complex.

Present address: Lab. de Spectroscopic des Mol&~les Diatomiques, CNRS UA779, Universit& des Scienceset Techniques de Lille, B&t. P5, 59655 Villeneuve dAscq Cedex, France.2 Alfred P. Sloan Fellow; Camille and Henry Dreyfus Teacher-Scholar.

261 0022-2852188 $3.00Copyright 0 1988 by Academic Press, Inc.All rights of reproduction in any form reserved.


2/11

262 DOUAY, NIETMANN, AND BERNATHTABLE I

The Observed Line Positions of the B A*-A II, Transition of C2 (in cm-)

3598.52353602.19973604.6484,605 87033605.87033604.63293602 16833598.4783593.55063567.38773579.99623571.37383561.51793550.4273353*.los7

188

-12-2526-3

3576.0043 -443556.4245 .43544.8056 43531.9682 -63517.9179 13SO2.6SO4 -303486.1780 13468.4925 -2

3408.2018 43385.7000 83361.9979 -33337.1040 31

4965.75124959.99064952.86264944.38484934.55184923.36474910.82224896.92714881.68014865.07854847.12944827.825,4807.17464785.11414761.62834737.1351

658

4945.6232 194934.1149 334921.2519 64907.0388 -304891.4832 -194874.5811 -1,4856.3371 44836.7461 -234815.8216 144,9,.552, -154169.9512 -34X5.0164 10

-2-4-5

0-6-39-321-120-1-9

-4133,-7

6-2

3-411

2

16-6 0

-8-86-41

-33509.7581

R.. cl-c Qr. o-c P.. o-c3596.2240 23600.5193 343603.5870 353605.4280 233606.0425 103605.4280 -193603.5870 -323600.5193 -233596.2240 43590.6971 1s3583.9356 -6,5,5.9458 -6

3588.87433586.12643582.154,3576.96173570.54713562.91233554.05663543.98123532.686,3520.17333506.44263491.49443475.33443457.9550X,9.,62,3419.5551,,98.54223376.3128

o-c o-c

2.0 6099.0536 13 6090.622,4.0 6102 0552 -15 6088 01216.0 6103 5729 69 6083 90966.0 6103 5726 -62 6078.313410.0 6102 094, 2 6071.226212 0 6099.11l3 -5 6062.646214.0 6094 6309 7 6052.577616.0 6088 6495 8 6041.018,le.0 6081 1684 1, 6027.964,20.0 6012.1796 -3, 6013.423522.0 6061.7003 19 5997.395224 0 5919.877226 0 - 5960.867928 0300 5918 4027

3571.57573561.79373550.78063538.56363525.1302,510.4836X94.62623477.560,Y459.28603439.80813419.12413397.2464

6067.05686055.854,6043.157,6028.97906013.31365996.17095977.52495957.44185935.86405912.8084

-272011-7

-32-8-214

-5232,556 27263544 5889

721 3374.16413349.8868

0 12

R.. o-c 91. o-c p.. o-c0. 32

25-20-1

6089.50816086.1526 -1,6081.3091 -6074.9741 26067.1482 -36057.833, 2604,.0309 196034.7L26 696020.9540 .6005.681* -2,5988.9280 -5970.684, -45950.9560 -75929.1439 2

6081.0760 -50bt o-c 6072.1124 176061.6512 -169.1 0-C P


3/11

TABLE I-Continued

-16244

-5

J R., o-c Qc . 0-C P,. o-c

o-c o-c err o-c -794,18-3,69

-22

4507.94764497.25w44*5.20604471.81574457.08664440.99664423.57944404.816,4384.7124

-22-18-80-1211-65

14495*

4524.*00, 04519.7129 -514513.277, -364505.4829 -744496.3456 04485.8476 24473.9944 -214460.796, ,o4446.2360 -364430.3319 -324413.0167 554,94.4,02 -86

Qc . 0-C

9 . 1

4,51.*6044749.4*,44745.75114740.66254734.21674726.41684717.2598478X.74754694.88074681.66044667.08724651.15884633.8796

4760 3878 10 4742.30514733.58564723.49854712.05654699.27154685.13724669.66914652.835,4634.6722L615.15984594.31604572.1,424548.6146

4165.64344766.23124765.46354763 32234759 82104754.96204748.72504741.12884732 1673

-11-12

519

-2,2821i

6,-4-709,10

o-c p.. o-c..4721.84794710.1430

4529.88284526.85324522.44344516.68784509.57944501.1239

-1914544 4502.7745 -8218 4491.4194 -15-5 4478.7137 1925 4464.6594 2,

0 4449.2510 -64-7 4432 5060 -99205. 4414.4626 287.21s 4395.0410 276.-43

J R.. o-c 9 ~ . 0-C P.. o-c 13.0 4540 3834 1915 017 0 4530.5649 -221 0 4758.2202 -29 19 0 4523 6463 288? 0 ir762 2134 2 4750.8375 -51 4,,*.,,54 28 21 0

5 0 L764 8500 4747.7934 6 4728.7014 29 23 0 4505 6376 687 0 4766.1192 -2 4743.3882 5 4717.9291 -21 25.0 r494.5965 369 0 4766.0326 -4 4737.6261 -1, 4705.812, 2 2, 011 0 4164.5903 46 4730.5128 4 4692. ,440 3 29 0

4467.656,4453.79384438.5556

-18404.08894384.8315


4/11

264 DOUAY, NIETMANN, AND BERNATHTABLE II

Observed Line Positions of the B Z&4 II, Transition of C2 (in cm - )A. O-0 BAND D. 1-2 BAND

J L. o-c P.. o-c .I Qef 0-C J R.. o-c p.. o-c J Q.r 0-C-48

-146

-57

-1-12

-5-9

-2110

6927.32396925.46296922.53866918.55076913.49796907.18146900.19916891.95336882.64196872.26246860.82816848.32696834.76496820.14216804.4626

-5-6-3

2-6-2-7

-50-404

-11-38

J R.. o-c P.. o-c J Q.r 0-C J R.. o-c P.. o-c .I Q.r 0-C

-2244

160-21

-151622 1 0 '

- 1-31

2 . 04 . 06 . 0B. 0

1 0 . 01 2 . 01 4 . 01 6 . 01 8 . 02 0 . 02 2 . 02 4 . 02 6 . 02 8 . 0

5204.01625202.54645200.14325196.86725192.71425187.68435181.79115175.0188516, ,7365158.85675149.470,5 1 3 9 . 2 1 7 55 1 2 8 0 9 6 05 1 1 6 . 1 0 8 ,

-1-5-310-5

-5210

3-1-5-22015-20

1.0 5340.8905 -36 1.0 8189.6339 63 0 5354.4885 -1 5333.8347 - 2 0 2 . 0 5 3 4 3 3 8 0 5 3 3 0 8 1 9 4 . 1 0 7 3 - 5 8 1 7 3 . 7 2 6 6 2 1 4 . 0 8 1 8 1 . 3 7 4 , - 3 05 0 5 3 5 8 . 3 0 4 5 1 2 5 3 2 5 . 8 5 6 2 5 4 . 0 5 3 4 1 . 7 5 8 0 - 4 8 1 9 7 . 5 0 2 0 1 3 8 1 6 5 . 4 7 6 5 1 6 6 0 8 1 7 8 . 4 0 4 3 - 1 97 0 5 3 6 1 . 1 8 7 6 - 6 5 3 1 6 . 9 5 4 2 2 2 6 . 0 5 3 3 9 . 2 0 9 , 8; , i

8 1 9 9 . 7 9 9 2 - 1 1 2 8 1 5 6 . 1 5 0 4 1 0 8 . 0 8 1 7 4 . 3 5 4 3 29 . 0 5 3 6 4 . 1 4 3 , 1 , 5 3 0 7 . 1 2 7 5 7 8 . 0 5 3 3 5 . 7 3 2 2 4 9 0 8 2 0 1 0 3 3 4 - 2 4 8 1 4 5 . 7 4 9 1 0 1 0 . 0 8 1 6 9 . 2 2 1 5 61 1 . 0 5 3 6 4 . 1 6 1 1 1 5 2 9 6 . 3 1 1 1 ( 1 7 1 0 . 0 5 3 3 1 . 3 2 9 1 2 1 8 2 0 1 1 7 5 5 0 8 1 3 4 . 2 1 4 0 - 9 1 2 . 0 8 1 6 3 . 0 0 7 8 1 11 3 . 0 5 3 6 4 . 2 5 1 5 1 7 5 2 1 4 . 7 1 7 5 1 , 1 2 . 0 5 3 2 5 . 9 9 4 9 7

; : , ;8 2 0 0 2 2 7 5 - 5 8 1 2 1 . 7 2 9 3 1 0 1 4 . 0 8 1 5 5 . 7 1 2 3 81 5 0 5 3 6 3 . 4 0 0 9 - 2 5 2 7 2 . 1 3 2 1 1 1 4 . 0 5 3 1 9 . 7 3 x 4 1 5 . 0 - 8 1 0 8 . 1 0 9 6 - 6 1 6 . 0 8 1 4 7 . 3 3 6 5 91 , 0 5 3 6 1 . 6 1 5 4 - 2 5 2 5 8 . 6 3 0 5 - 3 1 6 . 0 5 3 1 2 . 5 4 3 8 - 1 ; ; ; 8 1 9 5 . 0 6 9 2 3 8 0 9 3 . 4 2 1 5 - 1 0 1 8 . 0 8 1 3 7 . 8 7 9 , 1

1 9 . 0 5 3 5 8 . 8 9 1 5 - , I 5 2 4 4 . 2 1 3 2 - 5 1 8 . 0 5 3 0 4 . 4 2 6 2 - 2 8 1 9 0 8 5 7 0 8 8 0 7 7 . 6 6 6 8 - 1 2 0 . 0 8 1 2 7 . 3 4 2 0 - 2 52 1 . 0 5 3 5 5 . 2 2 9 2 - 2 1 5 2 2 8 . 8 . 9 1 1 - 1 1 2 0 . 0 5 2 9 5 . 3 7 9 , - 1 3 2 1 0 8 1 8 5 5 5 6 4 1 3 8 0 6 0 . 8 4 6 1 3 2 2 . 0 8 1 1 5 . 7 3 2 2 12 3 . 0 5 3 5 0 . 6 3 1 4 - 3 5 2 1 2 . 6 3 7 8 - 3 2 2 . 0 5 2 8 5 . 4 0 8 , 2 23 . 0 8 1 7 9 1 6 8 2 1 5 2 4 . 0 8 1 0 3 . 0 4 8 2 3 52 5 . 0 5 3 4 5 . 0 9 7 4 3 2 5 1 9 5 . 4 8 3 8 - 1 2 4 . 0 5 2 7 4 . 5 1 1 5 1 , 2 5 . 0 8 1 7 1 6 9 2 3 - 6 8 0 2 4 . 0 2 3 8 4 9 2 6 . 0 8 0 8 9 . 2 8 3 5 - 1 92 7 . 0 5 1 7 7 . 4 2 3 8 1 1 2 6 . 0 5 X2 . 6 8 7 8 1 2 2 7 . 0 8 1 6 3 1 4 0 3 3 0 * 0 * . 0 1 9 2 - 2 2 2 8 . 0 8 0 7 4 . 4 5 3 6 - 5 12 9 . 0 5 1 5 8 . 4 5 9 3 1 6 2 8 . 0 5 2 4 9 . 9 4 1 0 1 63 1 . 0 5 1 3 8 . 5 9 4 2 6 3 0 . 0 5 2 X. 2 7 6 6 - 6

3 2 . 0 5 2 2 1 . 6 9 8 2 - 1 F . 9 . 2 B AN D

c . 1 - O BA ND . I R . . O- C P . . O- C J 9 . c 0 - c

rL. 0-c P.. Q.f 0-c

2.04.06.08.0

10.012.014.016.018.020.022.024.026.028.0

8042.16198035.11658 0 2 , . 0 6 1 38 0 1 7 . 9 9 7 18 0 0 7 . 9 3 0 ,7 9 9 6 . 8 5 9 ,7 9 8 4 . 7 9 0 07 9 7 1 . 7 1 0 87 9 5 7 . 6 3 3 47 9 4 2 . 5 8 1 9

8044.55,8 -78042.,8,2 -448040.0107 -408036.2285 108 0 3 1 . 4 2 9 5 - 28 0 2 5 . 6 1 6 9 3 68 0 1 8 . 8 0 , 5 2 08 0 1 0 . 9 5 7 8 2 2

Note. Observed minus calculated line positions are in units of 10e4 cm-. Perturbed.


5/11

C2 BA,-A& AND BZ;-ArI.Cd

l-&,=6928 cm-

loo00

5000

0

IPhil lipsSystem I

V,= 8255 cm- II Esllik - RamsaySystam I II v,= 5522 cmIIz&-

IU31-I

265

FIG. 1. Energy level diagram of the low-lying states of C2.

Very recently, a new 1 A,, state was discovered by Goodwin and Cool ( 7). Two-photon fragmentation of acetylene followed by resonance-enhanced multiphoton ion-ization of CZ located the 1 A,, state 57 7 19 cm- above the X 2: state.

3595 cm- 3505 cm- FIG. 2. A portion of the O-O band of the B A,-A JTI. ransition of CZ near the R bandhead.


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266 DOUAY, NIETMANN, AND BERNATH

FIG 3. A portion of the O-O band of the B At-A II. transition of C, near the band origin.

II. EXPERIMENTThe experimental procedures are described in the previous paper (2).

III. RESULTS AND DISCUSSIONOur method of analysis is described in the paper on the Phillips system (2). The

spectra were very congested, so the analysis proceeded by bootstrap calculation. First,a crude estimate of the location of a band was made and some Q-branch lines werepicked out and assigned. A preliminary fit predicted the remaining lines in the bandwhich were then measured and included in the fit. The search for new bands wasguided by a preliminary calculation of Franck-Condon factors.Ultimately, eight bands of the B Ag-A III, transition were analyzed, O-O, l-0, 3-1, 5-2, O-l, 2-1, 4-2, and 3-2, while six bands were found for the B ?$-A II,transition, O-O, O-l, l-0, 1-2, 2-1, and 3-2. The line positions of the B A*-A II,and B X,+-X II, bands are reported in Tables I and II, respectively. An energy leveldiagram and sample spectra are provided in Figs. l-4.

C2 B.Z,- Ah,

FIG. 4. A portion of the O-O band of the B Et-AIn, transition of C, near the R bandhead.


7/11

C, BA,-AII, AND EZ;-A& 261TABLE III

Molecular Constants for the BA8 state of C2 (in cm-)COnStant v=0 =I v=2 v=3 =a v=5

T, lls59.o9so(2)~ 3243.6377(3) 14609.3115(4) 5944.1799(4) 17260.3030(12) 8553.7486(9)6" 1.45527S3(21) 1.4384277(24, 1.4215521(28) .4046420(30) 1.3877210(80) 1.~707393(81)

106 x 0" 6.3x.90(125) 6.34196(162) 6.3575(24) 6.3671(29) 6.4035(85) 6.3883(137)

a The numbers in parentheses are one standard deviation in the last digit.

The line positions of Tables I and II, as well as all of our observed line positions ofthe Phillips system (Table I of the preceding paper), were fitted simultaneously usingthe customary rotational energy level expression (2). The spectroscopic constants ofthe B A, and B Zi states from this global fit are reported in Tables III and IV,respectively.

The constants of the B A, state are very well behaved, but those of the B 2: stateshowed some evidence of interaction with other states. For example, o = 0, 1, and 2of the B Z,+ state required Hs, although none of the vibrational levels of theB A, state required any. The only local perturbations present in the B X&4 II,or the B*A,-AII, transitions are for u = 2, J = 19e, 21e of the lower AII,state (2).

The constants of Tables III and IV were converted to equilibrium molecular con-stants (Table V) with the expressions listed in the previous paper (2). The globalinteraction of the B Zgstate with other states (particularly the X Z,+ state) is alsoreflected in the equilibrium molecular constants (Table V). The W,X, value is verysmall (2.57 cm-) compared to the expected value of 7.65 cm- computed from (Y,with the Pekeris relationship (8). The G(u) and B, expansions require as many pa-rameters as data points to reproduce the data points within the experimental error inthe B Zg state.The X 2: and B ZJ states have the same symmetry, but nominally come fromdifferent configurations ( 1r4for X 2: and p2u2 for B Et). In the ground X 2:

TABLE IVMolecular Constants for the E 2: State of C2 (in cm-)

Constant v-0 v-1 v-2 v-3

T, 15196.5116(4)' 16616.9962(4) 1'3036.5144(8) 19457.8501(9)8" 1.4753124(42) 1.4648230(52) 1.4561354(112) 1.4478630(171)

10% D, 6.7810(95) 6.6208(137) 6.744(35) 6.881(63)lo'% H" 2.220(66) 2.167(107) 3.38(30)

' The numbers in parentheses are one standard deviation in the last digit


8/11

268 DOUAY, NIETMANN, AND BERNATHTABLE V

Equilibrium Molecular Constants for the B AZ and E I Zi States of C2 (in cm - )State . w.X. . Y.

B'A,B"ZZ+

B'A,B"X:

B'A,B"$

1407.46529(134)~ 11.47937(60) 0.010256(73)1424.11890b 2.57113b 0.46398b

B. 0. 7. x 106

1.4636853(34) 0.0168161(35) -1.503(72)1.481006(296) 0.011752(459) 67.1a(l387)

D, x 10e #J* 10'

6.3laa(l9) 0.1492(113)6.8596(136) -1.581(143)

=. -L

1.385475A 12082.3360(40)1.377350A 15409.1390(39)

a The numbers in parentheses are one standard deviation.b All xact fif.

TABLE VIRKR Turning Points of the B AC State of Cz

E (cm-) %,,(A) k,x (40.0 700.9482' 1.32618 1.452990.5 1396.0803 1.30375 1.483701.0 2085.4881 1.28732 1.508471.5 2769.1793 1.27398 1.530232.0 3447.1616 1.26260 1.550092.5 4119.4426 1.25259 1.560643.0 4786.0301 1.24363 1.586213.5 5446.9318 1.23549 1.603034.0 6102.1553 1.22802 1.619254.5 6751.7084 1.22111 1.634985.0 7395.5987 1.21467 1.65032a Relative to the bottom of the B'A, well. To convertthe origin of the E, scale to the bottom of the X1X:

well, 12082.1338 cm-', must be added. This numberwas calculated using the experimental value of11859.0980 cm-' for T,,. Note that the E, values inthis table include the Dunham Y,, correction for theB'A, state.


9/11

C, BA,-AII, AND BX;-x4&TABLE VII

RKR Turning Points for the B Z: State of Cz

269

E (cm-) %i, (A) %a, A)0.0 712.7427 1.31765 1.443480.5 1423.2797 1.29473 1.472681.0 2133.2272 1.27777 1.495751.5 2842.9331 I.26387 1.515582.0 3552.7454 1.25191 1.533312.5 4263.0120 1.24132 1.549503.0 4974.0809 1.23176 1.56448

a Relative to the bottom of the B"Cz Well. To convert theorigin of the E, scale to the bottom of the X18: well,15407.7529 cm-1 must be added. This number was calculatedusing the experimental T,, value of 15196.5116 cml. Notethat the E, values in this table include the Dunham Y,,correction for the B"x: state.

state, the G(u) and B, polynomial expansions are also not very satisfactory represen-tations of the vibrational and rotational energy levels. The interaction betweenX 2: and B Zi will change as a function of r and may cause the B 2: andX 2: potential energy curves to have peculiar shapes.The RKR potential energy curves (Tables VI and VII) were calculated from theequilibrium molecular constants (Table V). The RKR points for the B I Zg,B Ag, A II,, and X Zg states are plotted in Fig. 1 of the previous paper.The RKR potential points were used to calculate the B AZ-A II, (Table VIII) andB Zz-A II, (Table IX) Franck-Condon factors. We found all of the bands expectedon the basis of Franck-Condon factors, confirming our vibrational assignment.

TABLE VIIIFranck-Condon Factors for the B As-A II, Transition of Cz

0 0.544 EO 0.354 EO 0.898 E-l 0.113 E-l 0.754 E-3 0.253 E-4

1 0.306 EO 0.825 E-l 0.378 EO 0.193 EO 0.371 E-l 0.332 E-2

2 0.108 EO 0.263 EO 0.796 E-3 0.273 EO 0.270 EO 0.753 E-l

3 0.314 E-l 0.181 EO 0.138 EO 0.543 E-l 0.148 EO 0.307 EO

4 0.825 E-2 0.789 E-l 0.187 EO 0.409 E-l 0.122 EO 0.553 E-l

5 0.206 E-2 0.278 E-l 0.119 EO 0.146 ED 0.168 E-2 0.156 EO


10/11


11/11

C2 BL\,-A& AND BZ;-AII, 271ACKNOWLEDGMENTS

The National Solar Observatory is operated by the Association of Universities for Research in Astronomy,Inc., under contract with the National Science Foundation. We thank J. Wagner, R. Ram, and G. Ladd forassistance in acquiring our Cz spectra. Acknowledgment is made to the donors of the Petroleum ResearchFund, administered by the American Chemical Society, for partial support of this work. Some support wasalso provided by the Air Force Astronautics Laboratory, Grant No. F-046 1 -l 1187-K-0020.We thank J.Black for a copy of Ref. (6) and for discussions on the spectroscopic observations of C2 in space.RECEIVED: May 16, 1988

REFERENCES1. P. F. BERNATH,S. A. ROGERS,L. C. OBRIEN, C. R. BRAZIER,AND A. D. MCLEAN, Phys. Rev. Lett.

60, 197-199 (1988).2. M. D~UAY, R. NIETMANN, ND P. F. BERNATH, . Mol. Specfrosc. 131, 250-260 (1988).3. P. F. FONGEREAND R. K. NESBET,1. Chem. Phys. 44,285-298 (1966).4. J. BARSUHN,Z. Naturforsch.. A 27, 1031-1041 (1972).5. K. KIRBYAND B. Lru, J. Chem. Phys. 70,893-900 (1979).6. R. KLOTZ AND S. D. PEYERIMHOFF, rivate communication via J. Black and E. van Dishoeck.7. P. M. GOODWIN AND T. A. COOL,J. Chem. Phys. 88,4548-4549 (1988).8. G. HERZBERG, Spectra of Diatomic Molecules, 2nd ed., p. 108, Van Nostrand-Reinhold, New York,1950.

Documents

M. Douay et al- The Discovery of Two New Infrared Electronic Transitions of C2: B^1-Delta-g-A^1-Pi-u and B'^1-Sigma-g^+-A^1-Pi-u